











                           XT-4000S

                    Product Specification
                   and OEM Technical Manual























Document 1014995
Revision B
July 1989


                       REVISION RECORD



           Revision Date Published    Revised Contents



            01      April 1988        Preliminary Release
(originally released  as
revision A)



            02      May 1988          Preliminary Release



            03      July 1988         Preliminary Release


           A-1      August 1988       Formal Release

      A-1 (Adden 1) February 1989     Formal Release

      A-1 (Adden 2) April 1989        Formal Release



            B       July 1989         Formal Release

       B (Adden 1)  January 1990      Formal Release




                    Document No:  1014995

                           WARRANTY

Maxtor warrants  the XT-4000S  Family of  disk drives  against
defects in  materials and  workmanship for  a period of twelve
months, for  the original  purchaser.   Direct  any  questions
regarding the  warranty to  your Maxtor  Sales Representative.
Maxtor   maintains    Customer   Service   Centers   for   the
repair/reconditioning of  all Maxtor  products.    Direct  all
requests for  repair to the Maxtor Service Center in San Jose.
This assures you of the fastest possible service.
                     REGULATORY APPROVALS
         UL Recognition obtained:  File Number E87276(s)
         CSA Certification obtained:    File Number LR54048-6
         VDE Recognition obtained: File Number 41296G

Address comments concerning this manual to:

Maxtor Corporation
Technical Publications
211 River Oaks Parkway
San Jose, California 95134-1913
Telephone:  (408) 432-1700
Telex:  171074
FAX:  (408) 434-6469









Technical Data Restrictions

In case of sale to or use of units by DoD, use, duplication or
disclosure of  any software, firmware or related documentation
is subject to restrictions stated in paragraph (c) (1) (ii) of
the Rights  in Technical  Data and Computer Software clause at
DFAR 252.227-7013.   For Civilian Agencies: Use, reproduction,
or disclosure  of the  software and  related documentation  is
subject  to   restrictions  set   forth  in   FAR   52.227-19.
Unpublished rights  reserved under  the copyright  laws of the
United States.   Maxtor  Corporation, 211  River Oaks Parkway,
San Jose, CA 95134.








Copyright Notice

This manual  and all material contained in it are copyrighted.
The manual may not be copied, in whole or in part, without the
written consent  of Maxtor  Corporation.  The contents of
thismanual may be revised
without prior notice.

  Copyright 1988 by Maxtor Corporation, San Jose, California,
USA.  All rights reserved

PREFACE
Maxtor reserves  the right to make changes and/or improvements
to  its   products  without   incurring  any   obligation   to
incorporate such  changes or  improvements in units previously
sold or shipped.

Maxtor publishes descriptive Brochures and Data Sheets, an OEM
Manual, and a Quick Reference Guide for each product line.  In
addition, important  changes to  a product are conveyed in the
form of  a Technical Bulletin sent to all product customers of
record.   Changes that  affect the  content of  any manual arecovered by  publishing
addenda  or revisions  to the  affected
manual.
    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS

    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS


PREFACE.....................................................V


1.0..............................................INTRODUCTION
   1

  1.1.....................................General Description
      1
  1.2......................................Key Drive Features
      2
  1.3.................................Key Controller Features
      3
  1.4......................Summary of Supported SCSI Commands
      5

2.0.....................................SPECIFICATION SUMMARY
   7

  2.1..............................Performance Specifications
      7
  2.2...............................Functional Specifications
      8
  2.3............................Environmental Specifications
      9
  2.4.................................Physical Specifications
      9
  2.5..............................Reliability Specifications
      10
  2.6.......................Error Rates at the SCSI Interface
      10
  2.7...................................DC Power Requirements
      11
  2.8...............................Standards and Regulations
      11

3.0................................FUNCTIONAL CHARACTERISTICS
   13

  3.1.............................General Theory of Operation
      13  3.2......Read/Write Control and SCSI Controller Electronics
      13
  3.3.........................................Drive Mechanism
      14





Doc 1014995, Rev B           ix           Maxtor Corporation
Doc 1014995, Rev B           ix           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS

  3.4...................................Air Filtration System
      14
  3.5..............................Head Positioning Mechanism
      15
  3.6..............................Read/Write Heads and Disks
      16
  3.7.................................Track and Sector Format
      17
  3.8..........................................SCSI Interface
      17
     3.8.1....................Initiator-Target Configurations
          17
     3.8.2..............Logical/Electrical Signal Definitions
          19
     3.8.3......................Pin Assignments and Connector
          20
  3.9..............................Electrical Power Interface
      23
     3.9.1..................................Power-Up Sequence
          23
     3.9.2....................................Power Connector
          24
     3.9.3...................................Ground Connector
          25
  3.10..............................Mounting and Installation
      25
  3.11...............................................Shipping
      28

4.0...................................USER SELECTABLE OPTIONS
   29

  4.1.......................................SCSI ID Selection
      32
  4.2..................................Drive Power Up Options
      32  4.3..............................Terminator Power Selection
      33
  4.4....................................Write Protect Option
      34
  4.5...........................................Parity Option
      34
  4.6...........................................Other Jumpers
      34
  4.7.............................................Sector Size
      35
  4.8...................................Interface Termination
      35
  4.9.....................................Auxiliary Connector
      36





Doc 1014995, Rev B           x            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS

5.0...................................LOGICAL CHARACTERISTICS
   39

  5.1..................................Power Up and BUS RESET
      39
     5.1.1.................................Self-Test Sequence
          39
     5.1.2............................Initialization Sequence
          40
     5.1.3.................................Self Configuration
          41
     5.1.4...........................UNIT ATTENTION Condition
          41
  5.2........................................Buffering Scheme
      41

6.0..................................SCSI PHASES AND MESSAGES
   43

  6.1..........................................BUS FREE Phase
      44
  6.2.......................................ARBITRATION Phase
      45
  6.3.........................................SELECTION Phase
      45
  6.4.......................................RESELECTION Phase
      46  6.5.............................Information Transfer Phases
      47
     6.5.1..................Asynchronous Information Transfer
          48
     6.5.2..........................Synchronous Data Transfer
          48
     6.5.3......................................COMMAND Phase
          49
     6.5.4........................DATA IN and DATA OUT Phases
          50
     6.5.5.......................................STATUS Phase
          50
     6.5.6......................................MESSAGE Phase
          52
  6.6...........................................SCSI Messages
      52
     6.6.1...................................MESSAGE IN Phase
          52
     6.6.2..................................MESSAGE OUT Phase
          53
     6.6.3.............................COMMAND COMPLETE (00h)
          53
     6.6.4............................SAVE DATA POINTER (02h)
          54




Doc 1014995, Rev B           xi           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS

     6.6.5.............................RESTORE POINTERS (03h)
          54
     6.6.6...................................DISCONNECT (04h)
          54
     6.6.7.....................INITIATOR DETECTED ERROR (05h)
          54
     6.6.8........................................ABORT (06h)
          55
     6.6.9...............................MESSAGE REJECT (07h)
          55
     6.6.10................................NO OPERATION (08h)
          55
     6.6.11........................MESSAGE PARITY ERROR (09h)
          55
     6.6.12.....................LINKED COMMAND COMPLETE (0Ah)
          56
     6.6.13.........LINKED COMMAND COMPLETE (WITH FLAG) (0Bh)
          56     6.6.14............................BUS DEVICE RESET (0Ch)
          56
     6.6.15................................IDENTIFY (C0h/80h)
          56
     6.6.16...SYNCHRONOUS DATA TRANSFER REQUEST Message (01h)
          57
  6.7........................................Error Conditions
      59
     6.7.1.....................MESSAGE OUT Phase Parity Error
          59
     6.7.2.........................COMMAND Phase Parity Error
          60
     6.7.3........................DATA OUT Phase Parity Error
          60
     6.7.4...........................Initiator Detected Error
          60
     6.7.5...................................REJECTED Message
          61
     6.7.6.....................Initiator MESSAGE PARITY ERROR
          62
     6.7.7...............................RESELECTION Time-Out
          62
     6.7.8.........................Internal Controller Errors
          62

7.0.................................SCSI COMMAND DESCRIPTIONS
   61

  7.1...................................SCSI Command Overview
      61
  7.2.............................................FORMAT UNIT
      66





Doc 1014995, Rev B          xii           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS

     7.2.1.............................Defect List Management
          67
     7.2.2....................................SCSI Deviations
          68
     7.2.3.................................Command Parameters
          68
     7.2.4.......................................Format Modes
          70
     7.2.5..............................Initiator Defect List          75
       A..................................D List Block Format
          76
       B.......................D List Bytes from Index Format
          77
       C........................D List Physical Sector Format
          78
     7.2.6...................................Error Conditions
          80
  7.3.................................................INQUIRY
      82
     7.3.1....................................SCSI Deviations
          82
     7.3.2.................................Command Parameters
          82
     7.3.3........................................Data Format
          83
  7.4.............................................MODE SELECT
      87
     7.4.1....................................SCSI Deviations
          88
     7.4.2.................................Command Parameters
          88
     7.4.3..............................Parameter List Format
          89
       A.........................Parameter List Header Format
          89
       B...............Parameter List Block Descriptor Format
          90
       C...................................Page Header Format
          91
     7.4.4.....................Error Recovery Parameters Page
          92
     7.4.5..........................Disconnect-Reconnect Page
          99
     7.4.6.................................Format Device Page
          100
     7.4.7..........Rigid Disk Drive Geometry Parameters Page
          103
     7.4.8.......................................Caching Page
          105




Doc 1014995, Rev B          xiii          Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS
     7.4.9..........................Maxtor Drive Control Page
          107
     7.4.10...........................Read-Ahead Control Page
          109
     7.4.11..................................Error Conditions
          110
  7.5..............................................MODE SENSE
      112
     7.5.1....................................SCSI Deviations
          113
     7.5.2.................................Command Parameters
          113
     7.5.3..............................Parameter List Format
          115
       A.........................Parameter List Header Format
          116
       B...............Parameter List Block Descriptor Format
          117
       C...................................Page Header Format
          118
     7.5.4.....................Error Recovery Parameters Page
          118
     7.5.5...............Disconnect/Reconnect Parameters Page
          121
     7.5.6........Direct-Access Device Format Parameters Page
          123
     7.5.7..........Rigid Disk Drive Geometry Parameters Page
          126
     7.5.8.......................................Caching Page
          128
     7.5.9..........................Maxtor Drive Control Page
          130
     7.5.10................Read-Ahead Control Parameters Page
          132
     7.5.11..................................Error Conditions
          133
  7.6....................................................READ
      134
     7.6.1....................................SCSI Deviations
          134
     7.6.2.................................Command Parameters
          134
     7.6.3...................................Error Conditions
          135
  7.7.........................................READ (EXTENDED)
      136
     7.7.1....................................SCSI Deviations
          136
     7.7.2.................................Command Parameters
          136




Doc 1014995, Rev B          xiv           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual

                      TABLE OF CONTENTS

     7.7.3...................................Error Conditions
          137
  7.8.............................................READ BUFFER
      138
     7.8.1....................................SCSI Deviations
          138
     7.8.2.................................Command Parameters
          138
     7.8.3......................................Command Usage
          139
     7.8.4........................................Data Format
          139
     7.8.5...................................Error Conditions
          140
  7.9...........................................READ CAPACITY
      141
     7.9.1....................................SCSI Deviations
          141
     7.9.2.................................Command Parameters
          141
     7.9.3........................................Data Format
          142
     7.9.4...................................Error Conditions
          143
  7.10.......................................READ DEFECT LIST
      144
     7.10.1...................................SCSI Deviations
          144
     7.10.2................................Command Parameters
          144
     7.10.3............................................Header
          146
     7.10.4......................................Block Format
          147
     7.10.5...........................Bytes from Index Format
          148
     7.10.6............................Physical Sector Format
          149
     7.10.7..................................Error Conditions
          150
  7.11..............................................READ LONG
      151
     7.11.1...................................SCSI Deviations
          151     7.11.2................................Command Parameters
          151
     7.11.3..................................Error Conditions
          152
  7.12.....................................READ LONG (SCSI-2)
      153




Doc 1014995, Rev B           xv           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS

  7.13.........................READ MANUFACTURERS DEFECT LIST
      155
     7.13.1...................................SCSI Deviations
          155
     7.13.2................................Command Parameters
          155
     7.13.3.......................................Data Format
          156
  7.14.........................................REASSIGN BLOCK
      158
     7.14.1...................................SCSI Deviations
          158
     7.14.2................................Command Parameters
          158
     7.14.3................................Defect List Format
          159
     7.14.4..................................Error Conditions
          160
  7.15.............................RECEIVE DIAGNOSTIC RESULTS
      161
     7.15.1...................................SCSI Deviations
          161
     7.15.2................................Command Parameters
          161
     7.15.3.......................................Data Format
          162
     7.15.4..................................Error Conditions
          162
  7.16...........................................RELEASE UNIT
      163
     7.16.1...................................SCSI Deviations
          163
     7.16.2................................Command Parameters
          163
     7.16.3..................................Error Conditions
          164  7.17..........................................REQUEST SENSE
      165
     7.17.1...................................SCSI Deviations
          165
     7.17.2................................Command Parameters
          165
     7.17.3.......................................Data Format
          166
       A........................Nonextended Sense Data Format
          167
       B...........................Extended Sense Data Format
          167
       C..........................................Sense Codes
          173





Doc 1014995, Rev B          xvi           Maxtor Corporation
    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS

     7.17.4..................................Error Conditions
          177
  7.18...........................................RESERVE UNIT
      178
     7.18.1...................................SCSI Deviations
          178
     7.18.2................................Command Parameters
          178
     7.18.3..................................Error Conditions
          179
  7.19............................................REZERO UNIT
      180
     7.19.1...................................SCSI Deviations
          180
     7.19.2................................Command Parameters
          180
  7.20...................................................SEEK
      181
     7.20.1...................................SCSI Deviations
          181
     7.20.2................................Command Parameters
          181
     7.20.3..................................Error Conditions
          182
  7.21........................................SEEK (EXTENDED)
      183
     7.21.1...................................SCSI Deviations
          183     7.21.2................................Command Parameters
          183
     7.21.3..................................Error Conditions
          184
  7.22........................................SEND DIAGNOSTIC
      185
     7.22.1...................................SCSI Deviations
          185
     7.22.2................................Command Parameters
          185
     7.22.3..................................Error Conditions
          187
     7.22.4.......................................Subcommands
          188
       A..........................GET DRIVE STATUS Subcommand
          188
       B........................PASS DRIVE COMMAND Subcommand
          190
       C...............................READ HEADER Subcommand
          193
  7.23........................................START/STOP UNIT
      196





Doc 1014995, Rev B          xvii          Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS

     7.23.1...................................SCSI Deviations
          196
     7.23.2................................Command Parameters
          196
     7.23.3..................................Error Conditions
          197
  7.24........................................TEST UNIT READY
      198
     7.24.1...................................SCSI Deviations
          198
     7.24.2................................Command Parameters
          198
     7.24.3..................................Error Conditions
          198
  7.25.................................................VERIFY
      199
     7.25.1...................................SCSI Deviations
          199
     7.25.2................................Command Parameters          199
     7.25.3..................................Error Conditions
          200
  7.26..................................................WRITE
      201
     7.26.1...................................SCSI Deviations
          201
     7.26.2................................Command Parameters
          201
     7.26.3..................................Error Conditions
          202
  7.27.......................................WRITE (EXTENDED)
      203
     7.27.1...................................SCSI Deviations
          203
     7.27.2................................Command Parameters
          203
     7.27.3..................................Error Conditions
          204
  7.28.......................................WRITE AND VERIFY
      205
     7.28.1...................................SCSI Deviations
          205
     7.28.2................................Command Parameters
          205
  7.29...........................................WRITE BUFFER
      207
     7.29.1...................................SCSI Deviations
          207
     7.29.2................................Command Parameters
          207





Doc 1014995, Rev B         xviii          Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


                      TABLE OF CONTENTS

     7.29.3.......................................Data Format
          208
     7.29.4..................................Error Conditions
          209
  7.30.............................................WRITE LONG
      210
     7.30.1...................................SCSI Deviations
          210
     7.30.2................................Command Parameters
          210     7.30.3..................................Error Conditions
          211
  7.31....................................WRITE LONG (SCSI-2)
      212

APPENDIX A:  DISCONNECT/RECONNECT CONDITIONS..............215


APPENDIX B:  DEFECT MANAGEMENT............................217
  Reassignment Sequences..................................218
     Cylinder-Oriented Reassignment Sequence..............218
     Track-Oriented Reassignment Sequence.................220
     Drive-Oriented Reassignment Sequence.................220
     Host Defect Management Sequence......................221
  Defect Management Assumptions and Statistics............221

APPENDIX C:  CDB BIT DEFINITIONS..........................225


APPENDIX D:  UNITS OF MEASURE.............................227


APPENDIX E:  BUFFER RATIO APPLICATIONS....................229

  What are the Buffer Ratios?.............................229
  What are the Performance Benefits from Buffer Ratios?...229
  Buffer Full Ratio.......................................229
  Buffer Empty Ratio......................................231
  What value should be used for the Buffer Ratios?........231

APPENDIX F:  THE READ-AHEAD FEATURE.......................233

  What is Read-Ahead?.....................................233
  How Does it Work?.......................................233
  Key Read-Ahead Parameters...............................235
  Controlling the Read-Ahead Feature......................236
  Read Algorithm..........................................236
  Read-Ahead Performance..................................237

GLOSSARY..................................................239




Doc 1014995, Rev B          xix           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


                           FIGURES

    XT-4000S Product Specification & OEM Technical Manual

                           FIGURES

Figure 31..............................Air Filtration System
15
Figure 32.........................Head Positioning Mechanism
16
Figure 33.......................................Track Format
17
Figure 34........................Typical SCSI Configurations
18
Figure 35............Connector Locations, Rear View of Drive
22
Figure 36...............................SCSI Cable Connector
23
Figure 37...................Motor Start Current Requirements
24
Figure 38.......................................J3 Connector
25
Figure 39.............Mechanical Outline, Top and Side Views
26
Figure 310................Mechanical Outline, Isometric View
27
Figure 311...............................Removable Faceplate
28
Figure 41.........................................PCB Layout
29
Figure 42..................................Fab #3 PCB Layout
30
Figure 42A.................................Fab #6 PCB Layout
31
Figure 61..............Signal Sequence Chart for SCSI Phases
44
Figure 71...............Flow Chart of Automatic Reallocation
95
Figure E1.......Data Transfer Rate Without Buffer Full Ratio
230
Figure E2..........Data Transfer Rate With Buffer Full Ratio
231
Figure F1................Sequential Reads without Read-Ahead
234

    XT-4000S Product Specification & OEM Technical Manual


                            TABLES

    XT-4000S Product Specification & OEM Technical Manual


                            TABLES
Table 21..........................Performance Specifications
7
Table 22...........................Functional Specifications
8
Table 23................................Environmental Limits
9
Table 24.................................Physical Dimensions
9
Table 25..........................Reliability Specifications
10
Table 26.........................................Error Rates
10
Table 27...............................DC Power Requirements
11
Table 31...........................Connector Pin Assignments
21
Table 41.....................................SCSI ID Jumpers
32
Table 42.........................Summary of Power-Up Options
33
Table 43................Other Jumper Pin Assignments, Fab #1
34
Table 44................Other Jumper Pin Assignments, Fab #3
35
Table 45.................Auxiliary Connector Pin Assignments
36
Table 46.............Remote SCSI ID Programming Combinations
37
Table 61........................Signal States and Bus Phases
43
Table 62.....................................SCSI Bus Timing
47
Table 63.........................................Status Byte
50
Table 64........................................Status Codes
51
Table 65.......................................Message Codes
52
Table 66..............................IDENTIFY Message Codes
57
Table 67.......SYNCHRONOUS DATA TRANSFER REQUEST Byte Values
58
Table 68....Drive Responses to the SYNCHRONOUS DATA TRANSFER
REQUEST Message............................................58
Table 71.....................Typical CDB for 6-Byte Commands
61

    XT-4000S Product Specification & OEM Technical Manual


                            TABLES

Table 72....................Typical CDB for 10-Byte Commands62
Table 73...........................CDB Operation Code Format
63
Table 74.................................CDB Operation Codes
63
Table 75........................................Control Byte
64
Table 76.....................................FORMAT UNIT CDB
69
Table 77......................FORMAT UNIT Defect List Header
71
Table 78...................Initialization Pattern Descriptor
72
Table 79.....................Initialization Pattern Modifier
73
Table 710........................Initialization Pattern Type
73
Table 711.....................FORMAT UNIT Drive Format Modes
75
Table 712.........................FORMAT UNIT D List Formats
76
Table 713.....FORMAT UNIT Defect Descriptor(s), Block Format
77
Table 714.FORMAT UNIT Defect Descriptor(s), Bytes from Index
Format   78
Table 715..FORMAT UNIT Defect Descriptor(s), Physical Sector
Format   79
Table 716........................................INQUIRY CDB
82
Table 717..............................INQUIRY Response Data
84
Table 718................................MODE SELECT Command
88
Table 719..................MODE SELECT Parameter List Header
90
Table 720.MODE SELECT Parameter List Block Descriptor Format
91
Table 721.............................MODE SELECT Page Codes
92
Table 722..................Error Recovery Page (Page Code 1)
93
Table 723...................MODE SELECT Error Recovery Modes
98
Table 724..........................Disconnect-Reconnect Page
99
Table 725.................................Format Device Page
101
Table 726...MODE SELECT Rigid Disk Drive Geometry Parameters
(Page Code 4).............................................104

    XT-4000S Product Specification & OEM Technical Manual
                            TABLES

Table 727.......................................Caching Page
106
Table 728..........................Maxtor Drive Control Page
107
Table 729............Read-Ahead Control Page (Page Code 38h)
109
Table 730.................................MODE SENSE Command
113
Table 731.....................MODE SENSE Page Control Fields
114
Table 732..............................MODE SENSE Page Codes
115
Table 733...................MODE SENSE Parameter List Header
116
Table 734..MODE SENSE Parameter List Block Descriptor Format
117
Table 735..................MODE SENSE Page Header Page Codes
118
Table 736.MODE SENSE Error Recovery Parameters (Page Code 1)
119
Table 737.MODE SENSE Disconnect/Reconnect Control Parameters
(Page Code 2).............................................122
Table 738..MODE SENSE Direct-Access Device Format Parameters
(Page Code 3).............................................124
Table 739....MODE SENSE Rigid Disk Drive Geometry Parameters
(Page Code 4).............................................127
Table 740.................MODE SENSE Default Number of Heads
128
Table 741.......................................Caching Page
129
Table 742..........................Maxtor Drive Control Page
130
Table 743......Read-Ahead Control Parameters (Page Code 38h)
132
Table 744...........................................READ CDB
134
Table 745................................READ (EXTENDED) CDB
136
Table 746....................................READ BUFFER CDB
138
Table 747.................................READ BUFFER Header
140
Table 748..................................READ CAPACITY CDB
142
Table 749..........................READ CAPACITY Data Format
143
Table 750...............................READ DEFECT LIST CDB
144
Table 751...............READ DEFECT LIST Defect List Formats
146
    XT-4000S Product Specification & OEM Technical Manual


                            TABLES

Table 752............................READ DEFECT LIST Header
147
Table 753READ DEFECT LIST Defect Descriptor(s), Block Format
148
Table 754..READ DEFECT LIST Defect Descriptor(s), Bytes from
Index Format..............................................149
Table 755....READ DEFECT LIST Defect Descriptor(s), Physical
Sector Format.............................................150
Table 756......................................READ LONG CDB
152
Table 757..................................READ LONG Command
153
Table 758.................READ MANUFACTURERS DEFECT LIST CDB
156
Table 759..READ MANUFACTURERS DEFECT LIST Defect Descriptors
Returned Format...........................................157
Table 760.................................REASSIGN BLOCK CDB
159
Table 761..................REASSIGN BLOCK Defect List Header
159
Table 762................REASSIGN BLOCK Defect Descriptor(s)
160
Table 763.....................RECEIVE DIAGNOSTIC RESULTS CDB
161
Table 764...................................RELEASE UNIT CDB
163
Table 765..................................REQUEST SENSE CDB
166
Table 766........REQUEST SENSE Nonextended Sense Data Format
167
Table 767.........................Extended Sense Data Format
168
Table 768................................Field Pointer Bytes
170
Table 769...........................Actual Retry Count Bytes
170
Table 770...................Format Progress Indication Bytes
171
Table 771.............REQUEST SENSE Extended Sense Key Codes
172
Table 772.............................Additional Sense Codes
174
Table 773...................................RESERVE UNIT CDB
179
Table 774....................................REZERO UNIT CDB
180
Table 775...........................................SEEK CDB
181Table 776................................SEEK (EXTENDED) CDB
184

    XT-4000S Product Specification & OEM Technical Manual

                            TABLES

Table 777................................SEND DIAGNOSTIC CDB
186
Table 778............SEND DIAGNOSTIC Drive Self-Test Options
187
Table 779.........GET DRIVE STATUS Subcommand Parameter List
188
Table 780.......................GET DRIVE STATUS Data Format
189
Table 781.............GET DRIVE STATUS Command Status Values
190
Table 782.......PASS DRIVE COMMAND Subcommand Parameter List
191
Table 783..............PASS DRIVE COMMAND Status Data Format
192
Table 784...........PASS DRIVE COMMAND Command Status Values
192
Table 785...PASS DRIVE COMMAND Standard Status Response Bits
193
Table 786..............READ HEADER Subcommand Parameter List
194
Table 787............................READ HEADER Data Format
194
Table 788................TRANSLATE Subcommand parameter List
195
Table 789..............................TRANSLATE Data Format
195
Table 790................................START/STOP UNIT CDB
196
Table 791................................TEST UNIT READY CDB
198
Table 792.........................................VERIFY CDB
199
Table 793..........................................WRITE CDB
201
Table 794...............................WRITE (EXTENDED) CDB
203
Table 795...............................WRITE AND VERIFY CDB
205
Table 796...................................WRITE BUFFER CDB
208
Table 797......................Combined Header and Data Mode
209
Table 798.....................................WRITE LONG CDB
211
Table 799.................................WRITE LONG Command
212Table B1........................Defect Management Selections
218
Table B2.....................Spares Versus Capacity, XT-4380
222

    XT-4000S Product Specification & OEM Technical Manual


                            TABLES

Table B3.....................Spares Versus Capacity, XT-4170
223
Table E1.................................Buffer Ratio Values
232
Table F1......................................READ Algorithm
236
    XT-4000S Product Specification & OEM Technical Manual


                            TABLES




    XT-4000S Product Specification & OEM Technical Manual


1.0  INTRODUCTION


1.1  GENERAL DESCRIPTION

       The XT-4000S  Family disk  drives are  low cost,  high
       capacity,  high   performance,  random  access  storage
       devices which  use  nonremovable  5.25  inch  disks  as
       storage media.   Each disk surface employs one moveable
       head to  access the data tracks.  The total unformatted
       capacity  of  these  drives  ranges  from  179  to  384
       megabytes.

       The drives  include the Small Computer System Interface
       (SCSI) controller  embedded in  the drive  electronics.
       Some of  the resulting benefits of having an integrated
       controller  include   the  elimination  of  a  separate
       controller printed  circuit board  (PCB), reduction  in
       the number of associated cables, and elimination of the
       controller-specific power supply.

       Low cost  and high performance are achieved through the
       use of  a rotary  voice coil actuator and a closed loop
       servo system  using a  dedicated servo  surface.    The
       innovative MAXTORQ rotary voice coil actuator provides
       performance usually  achieved only  with larger, higher       powered linear
actuators.  The closed loop servo system
       and dedicated  servo surface  combine to allow state of
       the art  recording densities  (1,070 tracks  per  inch,
       21,064 bits per inch) in a 5.25 inch package.

       High capacity  is achieved by a balanced combination of
       high areal  recording density, run-length limited (RLL)
       data encoding  techniques, and  high density  packaging
       techniques.     Maxtor's  advanced  MAXPAK  electronic
       packaging  techniques   use  miniature  surface-mounted
       devices to allow all electronic circuitry to fit on one
       PCB.   Advanced flexures and heads allow closer spacing
       of disks,  and therefore allow a higher number of disks
       in a  5.25 inch  package.   Maxtor's unique  integrated
       drive motor/spindle  design allows  a deeper  head disk
       assembly (HDA)  casting than conventional designs, thus
       permitting eight disks to be used.

       The drive's electrical interface is compatible with the
       ANSI SCSI standard X3.131-1986, plus the Common Command
       Set (CCS)  requirements.   Size and mounting conform to
       the industry  standard 5.25 inch form factor for floppy
       and Winchester disk drives, and the same direct current
       (DC) voltages and connectors are used.

    XT-4000S Product Specification & OEM Technical Manual


1.2  KEY DRIVE FEATURES

       FEATURE                      BENEFITS

         Storage capacity  of 179  Ideal    for     multiuser
          to     384     megabytes  systems    and    graphics
          (unformatted)             workstations

         Single PCB                High reliability,  ease of
                                    maintenance

         Rotary    voice     coil  Fast,    accurate     head
          actuator and closed loop  positioning
          servo system

         Separate microprocessor-  Fast  access  times,  high
          controlled servo          reliability,   and    high
                                    density packaging

         Thin film metallic media  Higher  bit   density  and
                                    resolution, plus  improved
                                    durability

         Automatic actuator lock,  High   reliability,   data
          with   dedicated    head  protected from  mechanical          landing   and
shipping  shock
          zone

         Brushless   DC   spindle  Maximum storage capacity
          motor inside hub

         Separate microprocessor-  Precise   speed    control
          controlled spindle motor  under all load conditions

         Dynamic  braking  during  Minimum head/disk  contact
          power down cycle          time during spindown cycle

         Industry   standard   DC  Ease of integration
          power             supply
          requirements         (no
          alternating current (AC)
          power required)

         Industry        standard  Ease of integration
          physical    size     and
          mounting

         XT-4000S Product Specification & OEM Manual


1.3  KEY CONTROLLER FEATURES

       FEATURE                      BENEFITS

         Sophisticated, hardware-  Minimum time  on SCSI bus;
          based  control  of  SCSI  Maximum bus use
          protocol

         Up to  4.8 megabytes per  Maximum SCSI bus use
          second   data   transfer
          rate,     in      either
          asynchronous          or
          synchronous mode

         Synchronous  offsets  up  Provides     for      high
          to 15 bytes               performance on long cables
         High performance  buffer  Simultaneous          data
          manager                   transfers  from   disk  to
                                    buffer   and   buffer   to
                                    initiator

         In-line sector sparing    Maintains high performance
                                    over life  of drive,  even
                                    after             numerous
                                    reassignments

         Cylinder-oriented defect  Maximizes        formatted
          management                capacity   available    to
system

         Programmable    cylinder  No   slipped   revolutions
          skewing                   when   crossing   cylinder
                                    boundaries

         45 kilobytes dual ported  Maintains maximum SCSI bus
          first-in,      first-out  transfer rate
          buffer; two  full tracks
          capacity

         Hardware head switching   No head  skewing  required
                                    to     prevent     slipped
                                    revolutions     due     to
                                    software overhead

         Programmable              Flexibility;          more
          alternates/zones          available capacity

         Dedicated microprocessor  SCSI  bus   unaffected  by
          for SCSI                  drive interface functions,
                                    such as SEEK

         XT-4000S Product Specification & OEM Manual


         Error map on disk         Automatic           defect
                                    deallocation        during
                                    format; no manual entry

       FEATURE                      BENEFITS

         ANSI    SCSI    Standard  Compatibility;   ease   of
          X3.131-1986   Level    2  integration
          conformance

         Full  implementation  of  Availability  of   options
          CCS revision 4B           and industry compatibility

         Programmable   48    bit  High data integrity
          error  correction   code
          (ECC).

         Programmable   automatic  Flexibility and  high data
          retry on READ errors      integrity

         Interleave    of     1:1  Maximum data throughput
          supported

         Full                      Optimum      SCSI      bus
          disconnect/reconnect      performance
          capability
         Sector             sizes  User  flexibility;  system
          programmable from 180 to  compatibility
          4,096 bytes

         SCSI      implementation  Ease  of  integration  and
          compatible   with    all  upgrade
          Maxtor  Winchester   and
          optical drives

         XT-4000S Product Specification & OEM Manual
         XT-4000S Product Specification & OEM Manual



1.4  SUMMARY OF SUPPORTED SCSI COMMANDS

       The commands  supported by  the drive  are  listed  and
       discussed in  Section 7.0,  SCSI Command  Descriptions.
       For more  information on  Group 0  and Group 1 commands
       for direct-access  devices, see the reference documents
       below:

         ANSI X3.131-1986,  SCSI, American National Standards
          Institute, Inc., June 23, 1986.

         X3T9.2/85-52 Rev 4.B CCS,  June 23, 1986, a document
          of the American Standards Committee.

         XT-4000S Product Specification & OEM Manual




    XT-4000S Product Specification & OEM Technical Manual
    XT-4000S Product Specification & OEM Technical Manual



    XT-4000S Product Specification & OEM Technical Manual


2.0  SPECIFICATION SUMMARY


2.1  PERFORMANCE SPECIFICATIONS




                          Table 21
                  Performance Specifications


2.2  FUNCTIONAL SPECIFICATIONS




                          Table 22
                  Functional Specifications



2.3  ENVIRONMENTAL SPECIFICATIONS



                          Table 23
                     Environmental Limits



2.4  PHYSICAL SPECIFICATIONS




                          Table 24
                     Physical Dimensions



2.5  RELIABILITY SPECIFICATIONS




                          Table 25
                  Reliability Specifications

    XT-4000S Product Specification & OEM Technical Manual


2.6  ERROR RATES AT THE SCSI INTERFACE



                          Table 26
                         Error Rates



2.7  DC POWER REQUIREMENTS



                          Table 27
                    DC Power Requirements



2.8  STANDARDS AND REGULATIONS

       The Maxtor  XT-4000S Family  disk  drives  satisfy  the
       following standards and regulations:

       UNDERWRITERS LABORATORIES  (UL) = United States safety;
       UL 478,  Standard  for  Safety,  Electronic  Processing
       Units and Systems.

       CANADIAN STANDARDS ASSOCIATION (CSA) = Canadian safety;
       CSA C22.2  No. 220,  1986, Information  Processing  and
       Business Equipment (Consumer and Commercial Products).

       VERBAND  DEUTSCHER   ELECTROTECHNIKER  (VDE)  =  German
       safety; VDE  0806/8.81, Safety of Office Appliances and
       Business Equipment.

       INTERNATIONAL  ELECTROTECHNICAL   COMMISSION  (IEC)   =
       International  safety  commission;  IEC  950  (formerly
       380), Safety of Information Technology Equipment.

       FEDERAL COMMUNICATIONS COMMISSION (FCC) = United States
       radiation  emissions;  Part  15,  Subpart  J,  Class  B
       Consumer Computing Devices.

       CAUTION:     Connections between equipment must be made
       with shielded cables, and a shielded power cord must be
       used to connect AC power to the unit.

       CAUTION:     This equipment  generates and  uses  radio
       frequency energy,  and may  cause interference to radio
       and television  reception if  not installed and used in

    XT-4000S Product Specification & OEM Technical Manual


       strict accordance  with the instructions in this manual
       .

       The drive  has been tested and found to comply with the
       limits for  a Class  B computing  device, in accordance
       with the  specifications in Subpart J of Part 15 of FCC
       Rules,  which   are  designed   to  provide  reasonable
       protection  against   radio  and  television  reception
       interference in  a residential  installation.  However,       there is  no
guarantee that interference will not occur
       in a  particular installation.   If this equipment does
       cause interference  to radio  or television  reception,
       which can  be determined  by turning  the equipment off
       and on,  the user  is encouraged  to try to correct the
       interference  using   one  or  more  of  the  following
       measures:

         reorient the receiving antenna
         reorient the computer with respect to the receiver
         move the computer away from the receiver
         plug the  computer into  a different outlet, so that
         the computer  and receiver  are on  different  branch
         circuits

       If necessary,  consult the  dealer,  or  an  experience
       radio/television     technician,     for     additional
       suggestions.   You may  find the  FCC  booklet  How  to
       Identify and  Resolve Radio  TV  Interference  Problems
       helpful.   This booklet  is available  from the  United
       States Government  Printing Office,  Washington,  D.C.,
       20402, stock number 004-000-00345-4.

       Maxtor is  not responsible  for any radio or television
       interference caused  by unauthorized  modifications  to
       the drive.   It  is the  responsibility of  the user to
       correct such interference.
    XT-4000S Product Specification & OEM Technical Manual
    XT-4000S Product Specification & OEM Technical Manual
























































Doc 1014995, Rev B           1            Maxtor Corporation
Doc 1014995, Rev B           1            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


3.0  FUNCTIONAL CHARACTERISTICS


3.1  GENERAL THEORY OF OPERATION

       The disk  drive consists  of read/write,  control,  and
       interface electronics,  read/write heads, a servo head,
       a   head    positioning   actuator,    a   disk   drive
       motor/spindle, media,  and an  air  filtration  system.
       The components perform the following functions:

         interpret and generate control signals
         position the heads over the desired track         read and write data
         provide automatic error correction to the data
         provide a contamination-free environment
         provide a controller to interact with the initiator
         maintain precise spindle rotation speed


3.2  READ/WRITE CONTROL AND SCSI CONTROLLER ELECTRONICS

       All the  disk  drive  and  controller  electronics  are
       packaged on  a single  PCB.   This PCB,  which includes
       three  microprocessors,  performs  the  following  disk
       drive functions:

         data separation
         reading/writing of data
         index detection
         head positioning
         head selection
         disk drive selection
         fault detection
         track zero detection
         recalibration to track zero on power up
         track position counter
         power and speed control for spindle disk drive motor
         braking for the spindle disk drive motor
         disk drive up-to-speed indication
         reduced write current on the inner tracks
         monitoring for WRITE FAULT conditions
         control of all internal timing
         generation of SEEK COMPLETE signals
         RLL encoding/decoding

       The PCB performs the following controller functions:

         error detection and correction








Doc 1014995, Rev B           2            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


         SCSI bus disconnect/reconnect functions
         SCSI bus arbitration
         defect handling
         data transfer         automatic retries
         data buffering
         command linking
         sector formatting


3.3  DRIVE MECHANISM

       The  HDA   is  a   sealed  subassembly  containing  the
       mechanical portion  of the  disk drive.  A brushless DC
       disk drive  motor  contained  within  the  spindle  hub
       rotates the  spindle and  is controlled  by a dedicated
       microprocessor.   The motor and spindle are dynamically
       balanced to  ensure a  low vibration level, and dynamic
       braking is  used to quickly stop the spindle motor when
       power is removed.  The HDA is shock mounted to minimize
       vibration  through   the  frame.    The  frame  is  the
       mechanical assembly holding the HDA and PCB.


3.4  AIR FILTRATION SYSTEM

       The disks and read/write heads are assembled in a Class
       100 environment  and then  sealed within  the HDA.  The
       HDA contains  an absolute  filter, mounted  inside  the
       casting, to  provide constant  internal air  filtration
       (see Figure  31, Air  Filtration System).    A  second
       absolute filter,  located on the HDA top cover, permits
       pressure equalization between internal and ambient air.




                          Figure 31
                    Air Filtration System



3.5  HEAD POSITIONING MECHANISM

       The  read/write   heads  are   mounted  on  a  head/arm
       assembly, which  is then  mounted  on  a  ball  bearing
       supported shaft  (see F,  Head Positioning  Mechanism).
       The voice  coil,  an  integral  part  of  the  head/arm
       assembly, lies inside the magnet housing when installed
       in the  disk drive.   Current from the power amplifier,
       controlled by  the servo  system,  induces  a  magnetic
       field in  the voice  coil which  either aids or opposes




Doc 1014995, Rev B           3            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       the field  around the permanent magnets.  This reaction
       causes the  voice coil  to  move  within  the  magnetic
       field.   Because the  head/arm assemblies are connected
       to the  voice coil, voice coil movement is transferred,
       through the  pivot point,  directly to  the  heads,  to
       position them over the desired cylinder.




                          Figure 32
                  Head Positioning Mechanism


       Actuator movement  is controlled  by the servo feedback
       signal from  the servo  head.  The servo information is
       prewritten at  the factory  and is  used as  a  control
       signal for  the  actuator  to  provide  track  crossing
       signals  during   a  seek  operation,  track  following
       signals  during   on  cylinder  operation,  and  timing
       information, such  as index and servo clock.  The servo
       information also  provides the timing to divide a track
       into sectors  used for data storage.  The servo control
       system  has   a  dedicated   microprocessor  for  fast,
       optimized performance.


3.6  READ/WRITE HEADS AND DISKS

       The disk  drive employs  state of  the art  sliders and
       flexures.     The  configuration  of  the  sliders  and
       flexures  provides   improved  aerodynamic   stability,
       superior head/disk  compliance, and a higher signal-to-
       noise ratio.

       The disk  media uses  thin metallic  film, deposited on
       130  millimeter  diameter  aluminum  substrates.    The
       coating  formulation,   together  with   the  low  load
       force/low mass  heads, permits  highly reliable contact
       start/stop operation.   The nickel-cobalt metallic film
       yields high amplitude signals, and very high resolution
       performance,  compared  to  conventional  oxide  coated
       media.   It also  provides a highly abrasion and impact
       resistant surface,  decreasing the potential for damage
       caused by shock and vibration.

       Data on  each of  the data  surfaces  is  read  by  one
       read/write head;  each  head  accesses  1,224  physical       tracks.   There
is  one  surface  dedicated  to  servo
       information in each disk drive.






Doc 1014995, Rev B           4            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


3.7  TRACK AND SECTOR FORMAT

       The standard  track format  is organized  into numbered
       data  segments,  or  sectors  (see  Figure  33,  Track
       Format).   The sectors  are addressed  via the  logical
       block address  (LBA) in  the SCSI commands.  The method
       of encoding is 2, 7 RLL.




                          Figure 33
                         Track Format



3.8  SCSI INTERFACE


3.8.1     Initiator-Target Configurations

       The SCSI  initiator interface offers a number of unique
       advantages, facilitating  the  interconnection  of  the
       disk drive with one (or more) computer systems.  Unlike
       traditional  microcomputer  disk  interfaces,  such  as
       ST506, SCSI supports multiple peripherals and different
       peripheral  types,   all  operating  on  the  same  bus
       structure.   Figure 34,  Typical SCSI  Configurations,
       shows examples of typical configurations.




                          Figure 34
                 Typical SCSI Configurations


       The  disk   drive  also   supports  multiple  initiator
       configurations   consistent    with   the   established       arbitration
cycle  outlined  in  the  SCSI  standards.
       Configuration changes are made by SCSI address jumpers,
       which are  set when  the disk drive is installed in the
       system (jumper  settings are  discussed in Section 4.0,
       User Selectable Options).

       The SCSI  implementation used  in  the  disk  drive  is
       intended to facilitate high-speed data transfer between
       the initiator  and the  drive.  Interconnection between
       the initiator  system(s) and  the drive is via a fifty-
       pin   ribbon   cable,   and   uses   the   single-ended
       alternative, which  allows up  to  6  meters  of  cable
       length.





Doc 1014995, Rev B           5            Maxtor Corporation
    XT-4000S Product Specification & OEM Technical Manual


3.8.2     Logical/Electrical Signal Definitions

       The SCSI  bus uses  eighteen signals.  Nine signals are
       for the  8-bit data  bus, with one data parity bit; the
       other nine  signals are  the SCSI  control lines, which
       coordinate bus  accesses  for  transfers  of  commands,
       data, status,  and messages.  The interface signals are
       listed below;  refer to  the SCSI  standard for further
       details.  Pin assignments of the connector are provided
       in section 3.8.3, Pin Assignments and Connector.

       Across the SCSI bus all initiator signals are low-true.
       The signals  are asserted, or active, at 0 to 0.4 volts
       DC, and  negated, or inactive, at 2.5 to 5.25 volts DC.
       This low-true  logic is  indicated by the negative sign
       which precedes the signal name.

       -RST
       The -RST  (reset) signal  is an OR-tied signal asserted
       by the initiator, causing the disk drive to do a "hard"
       RESET,  self   configure,  and   return  to   the  IDLE
       condition.   This signal  is  normally  used  during  a
       power-up sequence.   The  -RST pulse should be at least
       25 microseconds wide.

       -SEL
       The -SEL  (select) signal is asserted by the initiator,
       along with  the disk  drive's SCSI ID bit (zero through
       seven), causing  the drive  to be  selected.   The -SEL
       line must  be negated  by the initiator after the drive       asserts  the   -
BSY  line   in  response  to  a  proper
       selection.   The signal  can be asserted by the arbiter
       (initiator or  disk drive)  in the  ARBITRATION  phase.
       The signal  is also  asserted by  the disk drive during
       the RESELECTION phase.

       -BSY
       The -BSY (busy) signal is an OR-tied signal asserted by
       the disk  drive, indicating that the bus is being used.
       It  is   also  asserted   by  the  arbiter  during  the
       ARBITRATION phase  and by  the initiator  and the  disk
       drive during the RESELECTION phase.

       -C/D
       Assertion of the -C/D (control/data) signal by the disk
       drive  indicates   that  command,  status,  or  message
       information is  to be  transferred  on  the  data  bus.
       Negation of  this line  indicates that  data is  to  be
       transferred on the data bus.








Doc 1014995, Rev B           6            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       -I/O
       When the  -I/O (input/output) signal is asserted by the
       disk drive it indicates that information is transferred
       to the  initiator from the disk drive.  Negation of the
       signal indicates that information is transferred to the
       disk drive  from the  initiator.   Note that  IN  means
       toward the initiator.

       -REQ
       When asserted  by the  disk drive,  the -REQ  (request)
       signal indicates  that a  byte is  to be transferred on
       the data  bus.   -REQ is negated following assertion of
       the -ACK line by the initiator.

       -ACK
       The  -ACK  (acknowledge)  signal  is  asserted  by  the
       initiator, following  assertion of  the -REQ  line,  to
       indicate data  has been  accepted by  the initiator, or
       that data is ready to be transferred from the initiator
       to the  disk drive.  -ACK is negated following negation
       of the -REQ line.
       -ATN
       The  -ATN   (attention)  signal   is  asserted  by  the
       initiator to indicate the ATTENTION condition, which is
       a request  for the  disk drive to enter the MESSAGE OUT
       phase.

       -MSG
       The -MSG (message) signal is asserted by the disk drive
       during one  of the  message phases.   Messages  may  be
       either IN  or OUT,  depending on  the state of the -I/O
       signal.

       -DB (7-0, P)
       The eight  bidirectional data  bus lines  (DB 7-0)  and
       parity line  (DBP) are  used to transfer 8 bit parallel
       data to/from  the initiator.   Bit  seven is  the  most
       significant bit.  Bits zero through seven are also used
       as SCSI  ID bits  during the ARBITRATION, SELECTION and
       RESELECTION phases.  Data bus parity (DBP) is odd.


3.8.3     Pin Assignments and Connector

       The disk  drive communicates  with an  initiator system
       via a  fifty-pin connector, J1.  The logical/electrical
       configuration of  the SCSI  connector is given in Table
       31, Connector  Pin Assignments.   Note  that the minus
       sign (-)  indicates low-true  logic, and  that all odd-
       numbered  pins   are  return   (ground)  pins  for  the
       associated even-numbered  pins, except  for pin twenty-





Doc 1014995, Rev B           7            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       five, which  is not  connected.   Pin one is located on
       the end  of J1  closest to  the DC power connector, J3.
       (See Figure  35, Connector  Locations,  Rear  View  of
       Drive.)



                          Table 31
                  Connector Pin Assignments




                          Figure 35
           Connector Locations, Rear View of Drive


       Connection to  J1 is  via a nonshielded fifty-conductor
       connector, consisting of two rows of twenty-five female
       contacts on  0.1 inch  centers.  Figure 36, SCSI Cable
       Connector, shows  the configuration and dimensions of a
       suitable mating  connector.   Recommended strain-relief
       connectors are  AMP part  number 1-499506-2,  or Dupont
       part  number  669002  (66900-250).    Use  of  a  keyed
       connector is recommended.




                          Figure 36
                     SCSI Cable Connector



3.9  ELECTRICAL POWER INTERFACE

       This section  describes the  power-up sequence  for the
       disk drive,  and the two connectors associated with the
       electrical power  interface.   These connectors are the
       power connector, J3, and the ground connector, J4.


3.9.1     Power-Up Sequence

       DC power  (+5 volts  and +12  volts) may be supplied in
       any order.   Both  power supplies  must be present, and
       within the  tolerances of  the power  sensing  circuit,
       before the  motor will  spin up.   Typical current draw
       during power  up is  shown in  Figure 37,  Motor Start






Doc 1014995, Rev B           8            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       Current Requirements.   When  the spindle  reaches full
       speed, the actuator lock automatically disengages.  The
       disk drive  performs automatic  SEEK calibration during       start up  for
optimum SEEK performance.  The disk drive
       executes its  recalibration sequence  whenever power is
       applied or  the START  STOP UNIT  command is  received.
       You may  delay starting  the spindle motor, to minimize
       power surges in multidrive configurations, by using the
       jumper  options   (see  section   4.2,  Drive  Power-Up
       Options).   The two  jumpers controlling the disk drive
       power up-options are also covered in this section.




                          Figure 37
               Motor Start Current Requirements



3.9.2     Power Connector

       The DC  power connector,J3  (shown in  Figure  38,  J3
       Connector) is  a four-pin  AMP  MATE-N-LOCK  connector,
       part  number   3505430-1.     The  recommended   mating
       connector is AMP part number 1-480424-0, using AMP pins
       part number  350078-4 (strip)  or part  number  61173-4
       (loose piece).   J3  pins are  numbered and assigned as
       shown in  Figure 38.  Figure 35, Connector Locations,
       Rear View  of Drive,  shows the  location of  J3 on the
       disk drive.




                          Figure 38
                         J3 Connector



3.9.3     Ground Connector

       The DC  logic ground  connector at the back of the HDA,
       J4, is  a Faston-type connector, AMP part number 61761-
       2.  (See Figure 35.)  The recommended mating connector
       is AMP  part number 62187-1.  If wire is used, the hole
       in J4  will accommodate  a maximum wire size of 18 AWG.
       This ground is optional.

       The frame  of the  disk drive is insulated from the HDA
       and the  DC logic  ground.   The frame  is electrically





Doc 1014995, Rev B           9            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       connected to  the computer  system chassis when mounted
       in a  computer system.  Normally the chassis, and hence
       the frame of the drive, is at earth ground.


3.10 MOUNTING AND INSTALLATION

       The disk  drive may  be mounted in any orientation.  In
       any  final  mounting  configuration,  ensure  that  the
       operation of  the three shock mounts, which isolate the
       HDA  from  the  frame,  is  not  restricted.    Certain
       switching power  supplies may emanate electrical noise,
       which can  degrade the  specified read error rate.  For
       best results,  orient the  disk drive  so that  the PCB
       assembly is not adjacent to these noise sources.
       Eight mounting  holes, four  on the  bottom and  two on
       each side,  are provided  for mounting  the disk  drive
       into an  enclosure.   The size  and location  of  these
       holes, shown in Figure 39, Mechanical Outline, Top and
       Side  Views,   are  identical  to  industry  standards.
       Overall height,  width, and depth, along with other key
       dimensions, are  shown in  Figure 39, and Figure 310,
       Mechanical Outline, Isometric.




                          Figure 39
            Mechanical Outline, Top and Side Views





                         Figure 310
              Mechanical Outline, Isometric View


       The faceplate  may be  removed in installations that do
       not require  it.  Remove the two E-Rings and unplug the
       light-emitting diode (LED) cable from the PCB, as shown
       in Figure 311, Removable Faceplate.



                         Figure 311
                     Removable Faceplate








Doc 1014995, Rev B           10           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


3.11 SHIPPING

       At power  down, the  heads are automatically positioned
       over the  nondata, dedicated  landing zone on each disk
       surface.   The automatic shipping lock solenoid is also
       engaged at  this time.   Maxtor ships the disk drive in
       single and  multipack shipping  containers.   Users can
       ship the  disk drive  installed when  the  nonoperating
       shock and vibration limits are not exceeded.














































Doc 1014995, Rev B           11           Maxtor Corporation
    XT-4000S Product Specification & OEM Technical Manual


4.0  USER SELECTABLE OPTIONS

       Jumper locations  for Fab  #1  (part  numbers  1015664,
       1015377, and 1014207) are identified in Figure 41, PCB
       Layout.




                          Figure 41
                          PCB Layout


       Jumper locations  for Fab  #3 (part numbers 1018353 and
       1018359) are  identified in  Figure  42,  Fab  #3  PCB
       Layout.




                          Figure 42
                      Fab #3 PCB Layout


































Doc 1014995, Rev B           44           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       Jumper locations  for Fab  #6 PCB (part number 1019822)
       are identified in Figure 42A, Fab #6 PCB Layout.




                         Figure 42A
                      Fab #6 PCB Layout



4.1  SCSI ID SELECTION

       SCSI ID  jumpers (JP35  through JP37)  are provided  to
       configure each  drive with  a SCSI device ID for use in
       multiple SCSI device configurations.

       Table 41,  SCSI ID  Jumpers, is  a reference table for
       the jumper  configuration, ID, and priority on the SCSI
       bus.   An ID  of seven  is the  highest priority  in  a
       multidevice configuration,  and is usually used for the
       initiator.




                          Table 41
                       SCSI ID Jumpers


       The drive is shipped from the factory with a SCSI ID of
       six.     This  assures   that  sufficient  jumpers  are
       available  for  any  address  except  seven,  which  is
       usually reserved for the host system.

       The SCSI  ID can  also  be  set  remotely  through  the
       auxiliary  connector,  as  mentioned  in  Section  4.9,
       Auxiliary Connector.   The  SCSI  ID  jumpers  must  be
       removed for this option and any shorting required for a
       selected SCSI ID is done outside the drive.


4.2  DRIVE POWER UP OPTIONS

       In order  to allow for system power supply constraints,
       which  may   require  minimizing   surge  current  when
       powering up  multiple drives,  three modes  of start up
       sequencing are  provided (see  Table  42,  Summary  of
       Power Up Options).








Doc 1014995, Rev B           45           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual




                          Table 42
                 Summary of Power-Up Options


       Start by ID Sequence:  With both JP14 and JP38 out, the
       drive delays  spinup for approximately 11 to 13 seconds
       times  the   SCSI  ID.     This  allows  for  power  up
       sequencing.   A RESET  condition results  in the  drive
       delaying its spinup according to its SCSI ID.

       Wait for Start Command:  With JP14 out and JP38 in, the
       drive does  not spin  up until  the initiator  issues a
       START STOP  UNIT command  with the  start bit  equal to
       one.

       Start When  Power Applied:  When JP14 is in and JP38 is
       out, the motor starts as soon as power is applied.  The
       drive is shipped in this configuration.

       NOTE: If the  drive has  JP14 in  and JP38 out, it does
       not respond to a START/STOP UNIT command.


4.3  TERMINATOR POWER SELECTION

       Power to  the terminators  may come internally from the
       drive, or externally from the SCSI bus.  If JP41 is in,
       the terminator  power is  internal, from the drive.  If
       JP34 is  in, the terminator power is external, from the
       SCSI bus.

       With  both  JP41  and  JP34  in,  terminator  power  is
       provided from  the drive  and to  the SCSI bus.  Hence,
       the  drive   is  at  one  end  of  the  SCSI  bus  with
       terminators in  place and  is also supplying terminator
       power for  the device  at the other end of the SCSI bus
       (see  Figure   34,   Typical   SCSI   Configurations).
       Additional discussion  of the  termination of  the SCSI
       bus and  location of  the drive on the bus is presented
       in Section 4.8, Interface Termination.

       As shipped,  JP41 is in and the drive supplies power to
       the terminators.  JP34 is out.


4.4  WRITE PROTECT OPTION

       The write protect jumper, JP18,  is used to protect the
       data written to the drive.  When the jumper is in, data
       cannot be  written on  the drive;  only READ operations
       can be  executed.   Installation of  JP18  grounds  the




Doc 1014995, Rev B           46           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       remote write  protect line, J2-7, forcing WRITE PROTECT
       on, and  prevents remote  control through  J2-7 on  the
       ten-pin connector.

       As shipped  from the  factory, JP18  is  out,  allowing
       normal  reading/writing,  or  optional  remote  control
       through the  J2 connector.   See Section 4.9, Auxiliary
       Connector, for details of the J2 connector.


4.5  PARITY OPTION

       The parity jumper, JP40, enables (in) or disables (out)
       odd parity  detection in  the drive.    Odd  parity  is
       always generated  by the drive and provided to the SCSI
       bus.

       The drive  is shipped  with JP40  in,  enabling  parity
       detection.


4.6  OTHER JUMPERS

       Other jumper  positions are not user selectable and are
       shipped as  indicated in Table 43 and Table 44, Other
       Jumper Pin Assignments.  The user should avoid changing
       these jumpers, or improper operation may occur.




                          Table 43
             Other Jumper Pin Assignments, Fab #1





                          Table 44
             Other Jumper Pin Assignments, Fab #3


       NOTE: Positions JP1,  JP2, JP3, JP8, JP9, JP32 and JP33
       are eliminated in the Fab #6 PCB.


4.7  SECTOR SIZE

       The drive  is shipped  from the  factory formatted with
       512 byte sectors.  Configuration parameters are default
       values in  all optional  cases.  It is recommended that
       users reformat  the drive  with the user's sector size,





Doc 1014995, Rev B           47           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       using  the   P  list,   and  the  user's  configuration
       parameters.


4.8  INTERFACE TERMINATION

       SCSI devices require proper interface termination.  The
       first device and the last physical, not SCSI ID, device
       on the  daisy chain  SCSI bus  must be  terminated (see
       Figure 34,  Typical SCSI  Configurations).  Remove the
       terminators from any devices in between.  For instance,
       if the drive is in the middle of the string, remove its
       terminators.   The disk  drive terminators are shown in
       Figure 41,  PCB Layout  and Figure  42,  Fab  #3  PCB
       Layout.

       Pin one  is on the end of the terminator that is marked
       with a  dot in  Figure 12, PCB Layout.  The orientation
       of the  terminator in  the PCB  is also  shown.    RN17
       through RN19  all look  like the side view inset in the
       figure.   Note that the hole/solder pad for pin one has
       a square  outline, whereas  all  others  have  a  round
       outline.     Pin  one  is  oriented  toward  the  power
       connector, J3.

       NOTE: All terminator  packs (RN17 through RN19) must be
       oriented with  the dot  toward J3 for the drive to work
       properly.

       As shipped,  interface signal lines are terminated with
       three removable 220/330 ohm resistor network packs.

       The devices  driving the  drive inputs  should be  open
       collector  devices  capable  of  sinking  at  least  48
       milliamps at  a voltage level of less than 0.5 volts DC
       (7438 or equivalent).

       Devices  receiving  the  drive  outputs  should  be  of
       SCHMITT trigger type to improve noise immunity, 74LS14,
       74LS240, or  equivalent.  The initiator should not load
       the bus  with more  than one standard low power Schotky
       transistor-transistor  logic  (LSTTL)  input  load  per
       line, and should terminate all signals with 220/330 ohm
       terminators.


4.9  AUXILIARY CONNECTOR

       Connector J2  in Figure  35, Connector Locations, Rear
       View of  Drive, is  an  auxiliary  connector  providing
       remote control  of  write  protect  and  SCSI  ID,  and
       ability to  carry the LED signal beyond the drive.  The





Doc 1014995, Rev B           48           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       auxiliary connector  is a Berg 68451-121, ten-pin part.
       The mating connector is a 3M 3473-6010 part.

       Pin  assignments   are  as   in  Table  45,  Auxiliary
       Connector  Pin   Assignments  (also   see  Figure  35,
       Connector Locations, Rear View of Drive).




                          Table 45
             Auxiliary Connector Pin Assignments


       When pin  seven is  connected to  ground, the  drive is
       protected from  writing, regardless of commands sent to
       the drive  via the  SCSI interface.   The write protect
       signal may  also be  connected  to  an  LED  whose  (+)
       terminal is  tied to  a voltage source, so that the LED
       is illuminated  when the  pin is grounded and the drive
       is in write protect mode.

       For remote  write protect,  JP18 must  be removed  (see
       Section 4.4, Write Protect Option).

       When an LED is connected to pin one (+) and pin five (-
       ), that  LED functions  in the  same manner  as the LED
       which is  mounted on the drive's front faceplate.  This
       is typically  used in  cases where the drive is mounted
       in a  position where the drive's LED is not visible and
       the faceplate is removed.

       Pin three  is not  present so  that users  can key  the
       mating connector.   Pin  three of  the mating connector
       should be blocked for this purpose.

       The SCSI  ID of the drive may be programmed remotely by
       selectively connecting  pins six,  eight,  and  ten  to
       ground, or leaving them open.  The various combinations
       are shown  in Table  46, Remote  SCSI  ID  Programming
       Combinations.




                          Table 46
           Remote SCSI ID Programming Combinations


       SCSI ID jumpers (JP35 through JP37) must be removed for
       the remote SCSI ID option.






Doc 1014995, Rev B           49           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
    XT-4000S Product Specification & OEM Technical Manual

























































Doc 1014995, Rev B           51           Maxtor Corporation
Doc 1014995, Rev B           51           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


5.0  LOGICAL CHARACTERISTICS

       The following  information is  based on  the ANSI  SCSI
       standard (X3.131-1986),  and the  Common   Command  Set
       (CCS).     For  more   information,  refer   to   these
       publications.


5.1  POWER UP AND BUS RESET

       The following  sections describe the sequence of events
       during drive  self-test and  initialization  sequences.
       The self-test sequence occurs before the initialization
       sequence.


5.1.1     Self-Test Sequence

       The self-test sequence is executed upon drive power up.
       The self-test  sequence verifies  the integrity  of the
       hardware.   This test  is not  an  exhaustive  hardware
       diagnostic, but  checks the  major components  for full
       function.   The drive does not respond to SELECTION for
       the first 250 milliseconds of the self-test.  After 250
       milliseconds  have   elapsed,  the  drive  responds  to
       SELECTION with  a BUSY  status for 2 to 3 seconds: this
       time  is   spent  completing  the  remaining  self-test
       sequences,  initializing   the  SCSI   circuitry,   and
       enabling the  SCSI interrupts.   After the self-test is
       complete and  the interface  circuitry  is  initialized
       (approximately  3   seconds),  the  drive  responds  to
       SELECTION  with   CHECK  CONDITION   status   and   the
       appropriate sense  data (i.e.,  UNIT  ATTENTION,  POWER
       ON/RESET condition).

       The  self-test   sequence  consists  of  the  following
       events:

         Hardware  Reset   Test  -  This  routine  tests  the
         microprocessor, buffer  controller,  disk  formatter,
         and  SCSI   reset  latch  for  the  proper  power  up
         condition.  If any of these tests fail, the drive can
         only be reset by a POWER UP condition.

         Microprocessor  Test   -  This   routine  tests  the
         microprocessor's   internal   memory,   timers,   and
         register bank switching for proper operation.

         Erasable  Programmable   Read  Only  Memory  (EPROM)
         Checksum Test  - This  routine  performs  a  checksum
         calculation on  the  controller  firmware  EPROM  and
         compares it against the checksum stored in the EPROM.




Doc 1014995, Rev B           52           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


         Buffer Controller  Test -  This  routine  tests  the
         buffer controller  for proper  operation.    All  the
         registers are  tested and  the  chip  is  engaged  to
         access random-access memory (RAM).

         Dynamic RAM  Test -  This routine  tests the dynamic
         RAM by  writing and  reading  different  patterns  to
         memory.  In addition, the buffer controller is tested
         for proper  refresh operation  and parity  detection.
         This test also tests the memory parity interrupt.

         Disk Formatter  Test -  This routine  tests the disk
         formatter chip  by writing  and reading  all possible
         patterns  to   each  of   the  disk   formatter  chip
         registers.   After  the  registers  are  tested,  the
         interrupts are  tested to  ensure that  the formatter
         chip generates an interrupt when a command completes.

         SCSI Controller  Test -  This routine tests the SCSI
         controller chip  by  executing  the  chip  diagnostic
         command.   After the  diagnostic test  completes, the
         interrupts are  tested to  ensure that  the SCSI chip
         generates an  interrupt  when  a  command  completes.
         Finally, the  registers are  tested  by  writing  and
         reading all  possible patterns  to each  of the  SCSI
         controller chip registers.

       If any  portion of  the  self-test  fails,  except  the
       hardware reset  test, the  drive can be reset by a SCSI
       bus RESET condition or a power up RESET condition.  The
       failure of  the hardware  reset test  is  considered  a
       catastrophic failure  and the  controller can  only  be
       reset  from   such  a  failure  by  a  power  up  RESET
       condition.


5.1.2     Initialization Sequence

       The initialization  sequence is executed for any one of
       the following three reasons:

         a POWER UP condition occurs
         the SCSI bus -RST signal is asserted
         a BUS  DEVICE RESET  message (on  the SCSI  bus)  is
       received

       After a  successful initialization,  the first  command
       from each  initiator is terminated with CHECK CONDITION
       status.   The sense data is set to UNIT ATTENTION/POWER
       ON, RESET, or BUS DEVICE RESET OCCURRED.

       Until the  drive has  spun up,  any command  sent by an
       initiator  which   requires  a  ready  drive  for  GOOD




Doc 1014995, Rev B           53           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       completion status,  is terminated  with CHECK CONDITION
       status.   The sense  data is  set to  DRIVE NOT  READY.
       Commands that  may complete  with GOOD  status prior to
       the drive  being  ready  are  REQUEST  SENSE,  INQUIRY,
       RESERVE UNIT,  RELEASE  UNIT,  START  STOP  UNIT,  READ
       BUFFER, and WRITE BUFFER.

       Note that  the INQUIRY  command results  in the general
       model designation  (XT-4000S) being  returned prior  to
       the drive  being READY.  Afterwards, the specific model
       number is returned.

       After a  RESET CONDITION occurs, the first command sent
       by the  initiator that causes a medium access loads the
       saved mode parameters into the current mode parameters.


5.1.3     Self Configuration

       When the  drive powers  up or a RESET CONDITION occurs,
       it  configures   itself   from   the   parameters   and
       information saved  on  the  medium  from  the  previous
       format operation.    This  includes  the  model  number
       returned  in   the  INQUIRY   command  and   the   mode
       parameters.   Refer to  7.4 MODE  SELECT, and  7.5 MODE
       SENSE later  in this  manual, which  describe the  mode
       parameters.


5.1.4     UNIT ATTENTION Condition

       A  UNIT  ATTENTION  condition  is  generated  for  each
       initiator whenever  the drive  has been reset (by a BUS
       DEVICE RESET message or a RESET condition), or when the
       mode parameters  have been changed by other initiators.
       The  UNIT   ATTENTION  condition   persists  for   each
       initiator until that initiator issues any command other
       than INQUIRY.   The  generation  of  a  UNIT  ATTENTION
       condition supercedes any pending sense data.

       If an  INQUIRY command  is received  from an  initiator
       with a  pending UNIT ATTENTION condition, the last UNIT
       ATTENTION generated  condition is  reported. The  drive
       returns the  INQUIRY data  and does not clear  the UNIT
       ATTENTION condition.


5.2  BUFFERING SCHEME

       The drive  has 64  kilobytes of  RAM.  The drive uses 4
       kilobytes of  RAM for a scratchpad, 16 kilobytes of RAM






Doc 1014995, Rev B           54           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual

       for a  write buffer  and 45,056 bytes of RAM for a data
       buffer.

       The drive will use the data buffer for read-ahead cache
       if this  feature is  enabled.   The drive  will use the
       data buffer for write operations if the transfer length
       exceeds 16 kilobytes.

       Normally, the  drive uses the split buffering, that is,
       separate buffers  for write  operations (write  buffer)
       and  read   operations  (data   buffer)   to   optimize
       throughput.    This  is  particularly  advantageous  in
       systems  that   perform   extensive   read-modify-write
       processes.

       The  buffer   controller  is   dual  parted,   allowing
       simultaneous transfers  to and  from the  initiator and
       the medium.







































Doc 1014995, Rev B           55           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
    XT-4000S Product Specification & OEM Technical Manual

























































Doc 1014995, Rev B           1            Maxtor Corporation
Doc 1014995, Rev B           1            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


6.0  SCSI PHASES AND MESSAGES

       The condition on the SCSI bus can be divided into eight
       distinct phases:

       BUS FREE phase
       ARBITRATION phase
       SELECTION phase
       RESELECTION phase
       COMMAND phase \
       DATA phase     \  These phases  are collectively termed
       the
       STATUS phase   /  Information Transfer phases.
       MESSAGE phase /

       The various phases are defined by the state of the SCSI
       bus signals  -SEL, -BSY,  -MSG, -C/D,  -I/O, -REQ,  and
       -ACK (see  Table 61,  Signal States  and Bus  Phases).
       The SCSI  bus can  never be in more than one phase at a
       time.   Figure 61,  Signal  Sequence  Chart  for  SCSI
       Phases, shows  the signal sequence of the eight phases.
       See the figure while reading the following sections.

       NOTE: The  condition   of   the   control   lines   for
       information transfer is valid  only when the SCSI bus -
       REQ signal  is asserted;  therefore, the  disk drive is
       not "in a phase" unless the --REQ signal is asserted.




                          Table 61
                 Signal States and Bus Phases





                          Figure 61
            Signal Sequence Chart for SCSI Phases



6.1  BUS FREE PHASE

       The BUS  FREE phase  is used  to indicate  that no SCSI
       device is  actively using  the SCSI bus, and that it is
       available for  subsequent users.   The  BUS FREE  phase
       occurs when  the drive  releases -BSY following a RESET
       condition or  certain  message  phases  (i.e.,  COMMAND
       COMPLETE and DISCONNECT).






Doc 1014995, Rev B           2            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


6.2  ARBITRATION PHASE

       The ARBITRATION  phase allows  one SCSI  device to gain
       control of  the SCSI bus so that it can assume the role
       of an  initiator or  target (drive).   The  arbitrating
       device waits  for the BUS FREE phase to occur.  It then
       asserts its  own SCSI ID bit and -BSY.  The arbitrating
       device then  examines  the  data  bus.    If  a  higher
       priority SCSI  ID bit  exists  on  the  data  bus,  the
       arbitrating device  loses arbitration and releases -BSY
       and the  data bus.   Otherwise,  the arbitrating device
       wins arbitration and asserts -SEL.

       NOTE: Implementation of  the  ARBITRATION  phase  is  a
       system option.   Systems  that do  not  implement  this
       option can  have only  one initiator.   The ARBITRATION
       phase  is   required   for   systems   that   use   the
       disconnect/reconnect feature.


6.3  SELECTION PHASE

       If  the  initiator  wins  arbitration,  it  enters  the
       SELECTION  phase   by  continuing  to  assert  its  own
       initiator SCSI ID bit and asserting the drive's SCSI ID
       bit.   The initiator  then negates  -BSY (-SEL  remains
       asserted by  the initiator).   If the initiator expects
       the drive  to disconnect/reconnect,  the initiator must
       assert the -ATN line prior to the negation of -BSY.

       If the initiator does not support arbitration, then the
       SELECTION phase  is entered  from the  BUS FREE  phase.
       The initiator asserts only the disk drive's SCSI ID bit
       and asserts -SEL.

       During the  SELECTION  phase,  the  drive  maintains  a
       negated -I/O  line so  that the  SELECTION phase may be
       distinguished from the RESELECTION phase.

       The drive  determines that  it  has  been  selected  by
       detecting its  SCSI ID  bit asserted  on  the  bus  (as
       determined by the ID jumpers, see 4.1 SCSI ID Selection
       earlier in this manual).

       If more  than two  IDs are asserted on the data bus, or
       parity is enabled and bad parity is detected, the drive
       does not respond to the SELECTION phase.

       The drive asserts -BSY after detecting that it has been
       selected.   At this  point, the initiator must negate -
       SEL and may remove the IDs from the data bus.






Doc 1014995, Rev B           3            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


6.4  RESELECTION PHASE

       After disconnecting to free the bus for other activity,
       the drive  reconnects when it is ready to transfer data
       or status across the bus.  The drive arbitrates for the
       bus and,  if it  wins, reselects  the initiator.    The
       RESELECTION phase  is similar  to the  SELECTION phase,
       except that  the -I/O  signal line  is asserted.    The
       drive asserts  its own  SCSI ID bit and the SCSI ID bit
       of the  initiator which is being reselected.  The drive
       releases  -BSY   (-BSY  was   already  asserted  during
       arbitration)  and   continues  to  assert  -SEL.    The
       initiator  detects   that  it  has  been  selected  and
       responds by asserting -BSY.  The drive detects that the
       -BSY signal  is now true and responds by also asserting
       -BSY (at  this point,  both the initiator and the drive
       are holding  the -BSY  signal low).   The   drive  then
       releases -SEL and the initiator responds by releasing -
       BSY (-BSY  is still  being asserted by the drive).  See
       Figure 61, Signal Sequence Chart for SCSI Phases.

       After reselecting  the initiator,  the drive  sends  an
       IDENTIFY message to identify itself to the initiator.

       If the  initiator does  not respond  to the reselection
       within a  selection time-out delay (see Table 62, SCSI
       Bus Timing),  the  drive  releases  the  bus  and  then
       rearbitrates  for  the  bus,  trying  to  reselect  the
       initiator.   It does this up to 255 times, or until the
       initiator responds or the drive is reset.

       NOTE: The   drive does  not disconnect  if, during  the
       SELECTION  phase,   the  initiator  does  not  set  its
       initiator  SCSI  device  ID  on  the  bus  and  if  the
       initiator does  not send  an IDENTIFY message out (with
       bit six asserted) to the drive.




                          Table 62
                       SCSI Bus Timing



6.5  INFORMATION TRANSFER PHASES

       The  -C/D,   -I/O,  and   -MSG  signals   are  used  to
       distinguish between  the different information transfer
       phases (COMMAND, DATA, STATUS, and MESSAGE).  The drive
       controls these  three signals, and, therefore, controls
       all changes  from one  phase to another.  The initiator





Doc 1014995, Rev B           4            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       can request  a MESSAGE OUT phase by asserting -ATN, and
       the   drive   can   cause   a   BUS   FREE   phase   by
       negating/releasing -SEL  and -BSY  (and all  other SCSI
       bus signals).

       The information  transfer phases use one or more -REQ/-
       ACK handshakes  to control  the  information  transfer.
       Each -REQ/-ACK  handshake allows  the transfer  of  one
       byte of  information.   During the information transfer
       phases, -BSY  remains  true  and  -SEL  remains  false.
       Additionally, during  the information  transfer phases,
       the  drive   continuously   envelopes   the   -REQ/-ACK
       handshake(s) with -C/D, -I/O, and -MSG in such a manner
       that these  control signals  are valid for a bus settle
       delay (see  Table 62,  SCSI  Bus  Timing)  before  the
       assertion of  -REQ of  the first  handshake, and remain
       valid until the negation of -ACK at the end of the last
       handshake.

6.5.1     Asynchronous Information Transfer

       The  drive   controls  the   direction  of  information
       transfer by  means of  the -I/O  signal.   When -I/O is
       true, information  is transferred from the drive to the
       initiator.     When  -I/O   is  false,  information  is
       transferred from the initiator to the drive.

       If -I/O  is true (transfer to the initiator), the drive
       first asserts  -DB (7-0,  P) to  their desired  values,
       delays at  least one  deskew delay,  plus a  cable skew
       delay (see  Table  62,  SCSI  Bus  Timing),  and  then
       asserts -REQ.   -DB (7-0, P) remain valid until -ACK is
       true at  the drive.   The  initiator reads -DB (7-0, P)
       after -REQ  is true, then signals its acceptance of the
       data by  asserting -ACK.  When -ACK becomes true at the
       drive, the  drive may  change or  release -DB (7-0, P),
       and negates  -REQ.   After -REQ is false, the initiator
       then negates  -ACK.  After -ACK is false, the drive may
       continue the  transfer by  asserting -DB (7-0, P) and -
       REQ as described above.

       If -I/O  is false  (transfer to  the drive),  the drive
       requests information  by asserting -REQ.  The initiator
       drives -DB  (7-0, P) to their desired values, delays at
       least one  deskew delay,  plus a  cable skew delay (see
       Table 62,  SCSI Bus  Timing), and  asserts -ACK.   The
       initiator continues to drive -DB (7-0, P) until -REQ is
       false.  When -ACK becomes true at the drive, the  drive
       reads -DB  (7-0, P)  and then  negates -REQ.  When -REQ
       becomes false  at  the  initiator,  the  initiator  may






Doc 1014995, Rev B           5            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       change or  release -DB (7-0, P), and negates -ACK.  The
       drive may  continue the  transfer by  asserting -REQ as
       described above.


6.5.2     Synchronous Data Transfer

       Synchronous data  transfer is optional, and may be used
       only if previously agreed to by the initiator and drive
       through the message system (see 6.6.16 SYNCHRONOUS DATA
       TRANSFER REQUEST  Message later  in this chapter).  The
       messages determine  the use  of synchronous mode by the
       initiator and  the drive,  and  establish  a  -REQ/-ACK
       offset and  a transfer  period.   The synchronous mode,
       once established, remains in effect for all DATA phases
       until a RESET condition or power cycle occurs, or until
       one of the devices elects to modify the agreement.

       The -REQ/-ACK  offset specifies the maximum number of -
       REQ pulses that can be sent by the target in advance of
       the number  of -ACK pulses received from the initiator,
       thereby establishing a pacing mechanism.  If the number
       of -REQ pulses exceeds the number of -ACK pulses by the
       -REQ/-ACK offset, the  drive does not assert -REQ until
       the next  -ACK pulse  is received.   A  requirement for
       successful completion  of the  DATA phase  is that  the
       number of -ACK and -REQ pulses be equal.

       The transfer  period specifies the minimum time allowed
       between leading  edges  of  successive  -REQ  and  -ACK
       pulses.

       The drive  asserts the -REQ signal for a minimum of one
       assertion period.  The drive waits at least the greater
       of a  transfer period  from the last transition of -REQ
       to true,  or the  minimum of a negation period from the
       last transition  of -REQ to false before the disk drive
       asserts the -REQ signal.

       The initiator  sends one  pulse of  the -ACK signal for
       each -REQ  pulse received.  The initiator asserts the -
       ACK signal  for a minimum of one assertion period.  The
       initiator waits  at least  the greater  of  a  transfer
       period from the last transition of -ACK to true, or for
       a minimum of a negation period from the last transition
       of -ACK to false, before the initiator asserts the -ACK
       signal.

       If -I/O  is true (transfer to the initiator), the drive
       first asserts  -DB (7-0,  P) to  their desired  values,
       waits at  least one  deskew delay,  plus one cable skew






Doc 1014995, Rev B           6            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       delay (see  Table  62,  SCSI  Bus  Timing),  and  then
       asserts -REQ.   -DB  (7+0, P)  are  held  valid  for  a
       minimum of one deskew delay, plus one cable skew delay,
       plus one  hold time (see Table 62) after the assertion
       of -REQ.   The  drive asserts -REQ for a minimum of one
       assertion period.   The  drive may then negate -REQ and
       change or  release -DB  (7-0, P).   The initiator reads
       the value  on -DB  (7-0, P) within one hold time of the
       transition  of  -REQ  to  true.    The  initiator  then
       responds with a -ACK pulse.

       If -I/O is false (transfer to the drive), the initiator
       transfers 1  byte for  each -REQ pulse received.  After
       receiving a -REQ pulse, the initiator first asserts -DB
       (7-0, P)  to the  desired value,  delays at  least  one
       deskew delay, plus one cable skew delay (see Table 62,
       SCSI Bus Timing), and then asserts -ACK.  The initiator
       holds -DB (7-0, P) valid for at least one deskew delay,
       plus one  cable skew  delay, plus  one hold  time  (see
       Table 62)  after the assertion of -ACK.  The initiator
       asserts -ACK  for a  minimum of  one assertion  period.
       The initiator  may then  negate -ACK  and may change or
       release -DB (7-0, P).  The drive reads the value of -DB
       (7-0, P) within one hold time of the transition of -ACK
       to true.

6.5.3     COMMAND Phase

       After  being   selected  and  processing  the  IDENTIFY
       message, if  any, the  drive normally  switches to  the
       COMMAND  phase.     The   6  or  10  bytes  of  command
       information (command  descriptor  block,  or  CDB)  are
       transferred from the initiator to the drive.

       If enabled, parity is checked on each command byte.  If
       bad parity  is detected,  the command  is aborted.  The
       drive switches  to  the  STATUS  phase,  returns  CHECK
       CONDITION status,  and sets  the sense  data to ABORTED
       COMMAND/PARITY ERROR  for that  initiator.   The  drive
       then switches  to the  MESSAGE phase, returns a COMMAND
       COMPLETE message, and goes to the BUS FREE phase.

       After each  command byte  transfer,  the  -ATN  bit  is
       checked; if  the -ATN line is active the drive switches
       to the  MESSAGE OUT phase and receives and then acts on
       the message.










Doc 1014995, Rev B           7            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


6.5.4     DATA IN and DATA OUT Phases

       In commands  that require  a DATA  phase (READ,  WRITE,
       MODE SELECT,  etc.), the  drive enters  a  DATA  phase.
       During the  DATA IN phase, data is transferred from the
       drive to  the initiator.   During  the DATA  OUT phase,
       data is transferred from the initiator to the drive.

       If bus  parity is  enabled and  bad parity is detected,
       the command is aborted.  The controller switches to the
       STATUS phase,  returns CHECK CONDITION status, and sets
       the sense data to ABORTED COMMAND/PARITY ERROR for that
       initiator.   The drive  then switches  to  the  MESSAGE
       phase, returns  a COMMAND COMPLETE message, and goes to
       the BUS FREE phase.

       After each  block, or  group of blocks, is transferred,
       the -ATN  bit  is  checked;  if  set,  the  disk  drive
       switches to  the MESSAGE phase to receive, and then act
       on, the message.


6.5.5     STATUS Phase

       After   completing   any   command   (successfully   or
       unsuccessfully, as  indicated by  the status byte), the
       drive switches  to the  STATUS phase  and  returns  the
       status byte  to the initiator.  The drive also switches
       to the STATUS phase for reporting a BUSY, INTERMEDIATE-
       GOOD, or  RESERVATION CONFLICT  status.  The drive does
       not go  to the  STATUS phase  if it is cleared by a BUS
       DEVICE RESET  or ABORT  message, or  by a  "hard" RESET
       condition.   Following  the  STATUS  phase,  the  drive
       enters the MESSAGE phase.

       The format  of the  status byte  containing the command
       completion information  is defined in Table 63, Status
       Byte.




                          Table 63
                         Status Byte


       The  reserved   bits   are   set   aside   for   future
       standardization and is always set to zero.

       The status  code field is used to specify the status of
       the completed  command.  Table 64, Status Codes, gives






Doc 1014995, Rev B           8            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       the bit  values for  the status  codes returned  by the
       disk drive.




                          Table 64
                         Status Codes


       Descriptions of the status codes are given below:

       GOOD -  This status  byte indicates  that the operation
       completed as expected.

       CHECK CONDITION  - Any  error, exception,  or  abnormal
       condition, that  causes sense  data to  be set causes a
       CHECK CONDITION  status.   The  REQUEST  SENSE  command
       should be  issued following a CHECK CONDITION status to
       determine the condition.

       NOTE:   If any  command other  than  REQUEST  SENSE  or
       INQUIRY is  issued following  a  CHECK  CONDITION,  the
       sense data is lost.

       BUSY -  The drive  returns this  status whenever  it is
       unable to  accept a  command.   For example,  the drive
       returns this  status when  it is  busy doing self-tests
       and self configuration after being powered up or reset,
       or if the drive is busy executing a previously received
       command.

       INTERMEDIATE-GOOD -  This status  is returned for every
       command in a series of linked commands (except the last
       command),  unless  an  error,  exception,  or  abnormal
       condition,  causes   a  CHECK  CONDITION  status  or  a
       RESERVATION  CONFLICT   status  to  be  set.    If  the
       INTERMEDIATE-GOOD status  is not returned, the chain of
       linked commands  is broken;  no further commands in the
       series are executed.

       RESERVATION CONFLICT - This status is returned whenever
       an  initiator  attempts  to  access  a  drive  that  is
       reserved by another initiator.


6.5.6     MESSAGE Phase

       The MESSAGE phase is used to transfer information about
       exception conditions  between  the  initiator  and  the
       drive.   The MESSAGE  IN and  MESSAGE  OUT  phases  are






Doc 1014995, Rev B           9            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       discussed below,  followed by  descriptions of the SCSI
       messages.   Message codes  supported by  the drive  are
       shown in Table 65, Message Codes.




                          Table 65
                        Message Codes



6.6  SCSI MESSAGES


6.6.1     MESSAGE IN Phase

       During the  MESSAGE IN  phase, a message is transferred
       from the  drive to  the initiator.  The drive may enter
       this phase at any time.


6.6.2     MESSAGE OUT Phase

       During the  MESSAGE OUT phase, a message is transferred
       from  the  initiator  to  the  drive.    The  initiator
       requests that  the drive enter the MESSAGE OUT phase by
       asserting the -ATN line.  The drive frequently monitors
       the -ATN  line and  enters the MESSAGE OUT phase at its
       earliest convenience  in response  to  the  initiator's
       assertion of -ATN.

       After being  selected, the drive sets the control lines
       in preparation  for the  MESSAGE OUT  phase.    If  the
       initiator has  -ATN  asserted,  the  drive  requests  a
       message from  the initiator  by asserting  -REQ.    The
       first message  is expected  to be  an IDENTIFY message,
       but the  drive also  accepts a  BUS DEVICE RESET, or an
       ABORT message.   If  any other  message is received the
       drive  goes  to  the  BUS  FREE  phase.    (See  6.6.16
       SYNCHRONOUS DATA TRANSFER REQUEST Message later in this
       chapter for additional information.)

       If, during the selection, the initiator does not assert
       its ID  on the bus, the drive does not examine the -ATN
       signal.  The drive assumes the initiator cannot support
       any message  except  COMMAND  COMPLETE,  and  does  not
       support DISCONNECT-RECONNECT.   The  drive also assumes
       the initiator ID is zero, and saves any status for that
       initiator as initiator zero.







Doc 1014995, Rev B           10           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       NOTE: If  the   initiator  expects   the     drive   to
       disconnect-reconnect, then  a MESSAGE  OUT  phase  (the
       IDENTIFY  message   with  bit   six  true)  must  occur
       immediately following  a SELECTION phase which had both
       the  initiator's,  and  the  drive's,  SCSI  device  ID
       asserted on the bus.


6.6.3     COMMAND COMPLETE (00h)

       The COMMAND  COMPLETE message is sent from the drive to
       the initiator  to indicate  that  the  execution  of  a
       command  (or   a  series   of  linked   commands)   has
       terminated, and  that valid status has been sent to the
       initiator.   After sending  this message  successfully,
       the   drive goes  to the  BUS FREE phase by releasing -
       BSY, unless the initiator sets the -ATN line.

       NOTE: The command  may or  may not  have been  executed
       successfully, as indicated in the status.

       If the  initiator rejects  this message  with a MESSAGE
       REJECT message,  the drive  goes to  the BUS FREE phase
       and does not consider this an error.


6.6.4     SAVE DATA POINTER (02h)

       When doing  disconnects, the  SAVE DATA POINTER message
       is sent  before every  DISCONNECT message  .    If  the
       initiator rejects  this message  with a  MESSAGE REJECT
       message, the drive does not disconnect.


6.6.5     RESTORE POINTERS (03h)

       The RESTORE  POINTERS message is sent from the drive to
       the initiator.   The  message acts  to restore  to  the
       active state  the most  recently saved pointers for the
       currently attached  logical  unit.    Pointers  to  the
       command, data,  and status  locations for  the  logical
       unit are  restored to the active pointers.  Command and
       status pointers  are restored  to the  beginning of the
       present command  and status areas.  The data pointer is
       restored to  the value  at the  beginning of  the  data
       area, or  to the  value at  the point at which the last
       SAVE DATA  POINTERS message  occurred for  that logical
       unit.

       If the  initiator rejects  this message  with a MESSAGE
       REJECT message,  the drive  immediately terminates  the
       present command  with a CHECK CONDITION status and sets





Doc 1014995, Rev B           11           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       the sense  data to  HARDWARE ERROR/MESSAGE REJECT ERROR
       (04h, 43h) for that initiator.

       When the  drive reselects  the initiator,  the IDENTIFY
       message implies  that the  initiator should restore its
       pointers.  Therefore, this message is not normally used
       in reselection.


6.6.6     DISCONNECT (04h)

       This message  is  sent  by  the  drive  to  inform  the
       initiator that the present physical path is about to be
       broken (the  drive plans  to disconnect  by releasing -
       BSY), but  that a  later reconnect is required in order
       to complete  the current  operation.  This message does
       not cause  the initiator  to save the data pointer.  If
       the initiator  rejects  this  message  with  a  MESSAGE
       REJECT message, the drive does not disconnect.


6.6.7     INITIATOR DETECTED ERROR (05h)

       The INITIATOR  DETECTED ERROR  message is  issued by an
       initiator  to  inform  the  drive  that  an  error  has
       occurred during  an operation.   This message should be
       sent by the initiator when a parity error is detected.


6.6.8     ABORT (06h)

       The ABORT  message is  sent from  the initiator  to the
       drive to clear the present operation.  All pending data
       and status  for the  issuing initiator  is cleared from
       the drive,  and the  drive goes  to the BUS FREE phase.
       Pending data  and status  for other  initiators is  not
       cleared.   No status  or ending message is sent for the
       operation.  It is not an error to issue this message to
       a logical  unit that  is not  currently  performing  an
       operation for the initiator.


6.6.9     MESSAGE REJECT (07h)

       The MESSAGE  REJECT message  is sent  from  either  the
       initiator or  the  drive  to  indicate  that  the  last
       message received  was inappropriate  or  has  not  been
       implemented.

       To  create  a  MESSAGE  REJECT  message  the  initiator
       asserts -ATN  prior to releasing -ACK; the handshake of






Doc 1014995, Rev B           12           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       the message  is then  rejected.   When the  drive sends
       this message  it changes  to the  MESSAGE IN  phase and
       sends  this  message  prior  to  requesting  additional
       message bytes  from the  initiator.   This provides  an
       interlock so  that the  initiator can  determine  which
       message is rejected.

       If the  initiator  responds  to  this  message  with  a
       MESSAGE  REJECT   message,  the     drive   immediately
       terminates the  present command  with a CHECK CONDITION
       status  and   sets   the   sense   data   to   HARDWARE
       ERROR/MESSAGE ERROR (04h, 43h) for that initiator.


6.6.10    NO OPERATION (08h)

       The initiator  sends the  NO OPERATION  message when it
       has no  valid message for the drive request.  The drive
       receives and ignores this message.


6.6.11    MESSAGE PARITY ERROR (09h)

       The initiator  sends a  MESSAGE PARITY ERROR message to
       indicate a  parity error  on one  or more  bytes of the
       last message  sent  from  the  drive.    The  initiator
       asserts -ATN  prior to releasing -ACK for the last byte
       of the  message in error, so that the drive knows which
       message is  in error.   The  drive resends the message.
       If the  Message Parity  Error is  received  again,  the
       drive goes to the BUS FREE phase and aborts the current
       command for that initiator.  No further reconnection is
       attempted, and  neither  STATUS  nor  COMMAND  COMPLETE
       messages are  returned for the command.  The sense data
       is set  to ABORTED COMMAND/SCSI PARITY ERROR (04h, 47h)
       for that initiator.


6.6.12    LINKED COMMAND COMPLETE (0Ah)

       The LINKED  COMMAND COMPLETE  message is  sent  to  the
       initiator to  indicate that  the execution  of a linked
       command has  completed and  that the  status  has  been
       sent.

       If  the   initiator  responds  with  a  MESSAGE  REJECT
       message, the  drive goes to the BUS FREE phase and does
       not execute the next command.  The sense data is set to
       HARDWARE ERROR/MESSAGE  ERROR    (04h,  43h)  for  that
       initiator.






Doc 1014995, Rev B           13           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


6.6.13    LINKED COMMAND COMPLETE (WITH FLAG) (0Bh)

       The LINKED COMMAND COMPLETE (WITH FLAG) message is sent
       to the  initiator to  indicate that  the execution of a
       linked command  (with the  flag bit  set  to  one)  has
       completed and that the status has been sent.

       If  the   initiator  responds  with  a  MESSAGE  REJECT
       message, the  drive goes to the BUS FREE phase and does
       not execute the next command.  The sense data is set to
       HARDWARE ERROR/MESSAGE ERROR (04h, 43h).


6.6.14    BUS DEVICE RESET (0Ch)

       An initiator  may send  the BUS DEVICE RESET message to
       the drive  to clear  all current  commands on that SCSI
       device.   The drive  clears all  commands, goes through
       its initial  power up  checks, its  self configuration,
       and goes to the BUS FREE condition ("hard" RESET).


6.6.15    IDENTIFY (C0h/80h)

       The IDENTIFY  message is  sent by an initiator after it
       selects a  drive.  It is sent by the drive as the first
       message  after  a  reconnection.    In  addition,  this
       message specifies  that the sender supports some or all
       of the  optional messages.   The  bits  in  Table  66,
       IDENTIFY  Message  Codes,  show  that  the  only  truly
       changeable bit  is bit  six; therefore, the command can
       have only  two values:  C0h if the disconnect/reconnect
       feature    is     supported,    or     80h    if    the
       disconnect/reconnect feature is not supported.




                          Table 66
                    IDENTIFY Message Codes


       If the  initiator  responds  to  this  message  with  a
       MESSAGE   REJECT   message,   the   drive   immediately
       terminates the  present command  with a CHECK CONDITION
       status and  sets the  sense key/error  code to HARDWARE
       ERROR/Message  Reject   Error  (04h,   43h)  for   that
       initiator.

       NOTE: The drive  does not  disconnect  if,  during  the
       SELECTION  phase,   the  initiator  does  not  set  its
       initiator SCSI  device  ID  on  the  bus,  and  if  the




Doc 1014995, Rev B           14           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       initiator does  not send  an IDENTIFY message out (with
       bit six set) to the drive.


6.6.16    SYNCHRONOUS DATA TRANSFER REQUEST Message (01h)

       The drive  can, optionally,  perform  synchronous  data
       transfers,  as  discussed  in  6.5.2  Synchronous  Data
       Transfer  earlier   in  this   chapter.     A  pair  of
       SYNCHRONOUS DATA  TRANSFER REQUEST  messages (see Table
       67 SYNCHRONOUS  DATA TRANSFER REQUEST Byte Values) are
       exchanged between  an initiator and the drive under the
       following conditions:

         a  SCSI   device  that   supports  synchronous  data
         transfer recognizes  it has not communicated with the
         other SCSI  device since  receiving the  last  "hard"
         RESET

         A  SCSI   device  that   supports  synchronous  data
         transfer recognizes  it has not communicated with the
         other SCSI  device since receiving a BUS DEVICE RESET
         message

       SCSI devices  may also  exchange messages  to establish
       synchronous data transfer when requested to do so.  The
       messages exchanged  establish the  transfer period  and
       the -REQ/-ACK offset.




                          Table 67
        SYNCHRONOUS DATA TRANSFER REQUEST Byte Values


       The transfer  period is  defined as  the  minimum  time
       between the  leading edge  of a  -REQ pulse  and of its
       corresponding -ACK  pulse.   The  -REQ/-ACK  offset  is
       defined as  the maximum  number of -REQ pulses that may
       be outstanding  before the  corresponding -ACK pulse is
       received at  the drive.   A  -REQ/-ACK offset  value of
       zero indicates asynchronous mode; a value of 0Fh yields
       the maximum number of outstanding -REQ pulses supported
       (fifteen).

       If  the   initiator  recognizes   that  negotiation  is
       required, it  asserts -ATN and, if the drive implements
       message transfers,  sends a  SYNCHRONOUS DATA  TRANSFER
       REQUEST message,  specifying the  -REQ/-ACK offset  and
       minimum transfer  period.    The  -REQ/-ACK  offset  is






Doc 1014995, Rev B           15           Maxtor Corporation
    XT-4000S Product Specification & OEM Technical Manual


       chosen to  meet the  data handling  requirements of the
       target, while  the minimum transfer period is chosen to
       meet the  data handling  requirements of the initiator.
       The drive responds in any of the ways outlined in Table
       68, Drive  Responses to  the SYNCHRONOUS DATA TRANSFER
       REQUEST Message.




                          Table 68
   Drive Responses to the SYNCHRONOUS DATA TRANSFER REQUEST
                           Message


       The implied  agreement remains  in effect  until a  BUS
       DEVICE  RESET  message  is  received,  a  "hard"  RESET
       condition occurs,  or until one of the two SCSI devices
       elects to modify the agreement.  Renegotiation at every
       selection  is   not  recommended  since  a  significant
       performance impact is likely.  The default mode of data
       transfer is  asynchronous.  The default mode is entered
       at power on, after a BUS DEVICE RESET message, or after
       a  "hard"   RESET  condition.    The  SYNCHRONOUS  DATA
       TRANSFER REQUEST  message exchange  can only take place
       following a  SELECTION phase that includes the SCSI IDs
       for both  the initiator  and the  target.  Violation of
       this rule  may make  data transfer  impossible owing to
       disagreements  among   SCSI  devices   about  the  data
       transfer mode.


6.7  ERROR CONDITIONS

       Under several  error conditions,  the drive changes the
       phase to  BUS FREE  without correctly  terminating  the
       command  (i.e.,   no  DISCONNECT  or  COMMAND  COMPLETE
       message is  sent).   The drive  clears all  information
       regarding the  command, except sense data (if any), and
       does not  attempt to  reconnect, or  in any  other  way
       terminate, the command.  The initiator must assume that
       this is  a catastrophic failure and return the error to
       the system software.

       Sense data  may or may not be valid when this condition
       occurs.   If  the  initiator  issues  a  REQUEST  SENSE
       command and the returned sense key and additional sense
       code are not zero, the sense data is valid.









Doc 1014995, Rev B           16           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


6.7.1     MESSAGE OUT Phase Parity Error

       If the  drive detects a parity error during the MESSAGE
       OUT phase  it retries  the MESSAGE OUT phase once using
       the following sequence:

       1. Continue the -REQ/-ACK handshake until the initiator
          negates -ATN (receives all of the message bytes).

       2. Instruct the  initiator to resend all of the message
          bytes sent  during the previous MESSAGE OUT phase by
          not changing the phase and asserting -REQ.

       3. The initiator  then  resends  all  of  the  previous
          message bytes.

       If, after  one retry, the message is still not received
       correctly, the  drive processes  the error using one of
       the following sequences:

         If an  IDENTIFY message  is not  received, the drive
          immediately goes  to the  BUS FREE  phase.  No sense
          data code information is set for this type of error.

         If  an  IDENTIFY  message  is  received,  the  drive
          terminates  the   present  command   with  a   CHECK
          CONDITION status  and sets the sense data to ABORTED
          COMMAND/SCSI PARITY  ERROR (0Bh/47h).    This  error
          does not  prevent the  initiator from  retrying  the
          command.


6.7.2     COMMAND Phase Parity Error

       When the  drive  detects  a  parity  error  during  the
       COMMAND phase,  it retries  the COMMAND  phase one time
       using the following sequence:

       1. Send the  initiator a  RESTORE POINTERS  message  to
          reset the pointers to the start of the command.

       2. Attempt to receive the entire command again.

       If, after  one retry, the command is still not received
       successfully, the drive aborts the command using one of
       the following sequences:

         If the  initiator does not send an IDENTIFY message,
          the drive  immediately goes  to the  BUS FREE phase.
          No sense  data  information is sent for this type of
          error.






Doc 1014995, Rev B           17           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


         If  the  drive  receives  an  IDENTIFY  message,  it
          terminates the command with a CHECK CONDITION status
          and sets  the sense  data  to  ABORTED  COMMAND/SCSI
          PARITY ERROR (0Bh/47h).  This error does not prevent
          the initiator form retrying the command.


6.7.3     DATA OUT Phase Parity Error

       If the drive detects a parity error during the DATA OUT
       phase, it terminates the command with a CHECK CONDITION
       status, and sets the sense data to ABORTED COMMAND/SCSI
       PARITY ERROR(0Bh/47h).  This error does not prevent the
       initiator from retrying the command.


6.7.4     Initiator Detected Error

       If the  drive  receives  an  initiator  detected  error
       message at  any time  during the command, except during
       the  STATUS  phase  or  COMMAND  COMPLETE  message,  it
       terminates the  current command  with a CHECK CONDITION
       status   and   sets   the   sense   data   to   ABORTED
       COMMAND/INITIATOR      DETECTED      ERROR      MESSAGE
       RECEIVED(0Bh/48h).   This error  does not  prevent  the
       initiator from retrying the command.

       If the  initiator sends  an  initiator  detected  error
       message immediately  after the  STATUS phase, the drive
       sends  a  RESTORE  POINTERS  message  and  resends  the
       status.   If  the  initiator  sends  another  initiator
       detected  error  message  in  response  to  the  resent
       status, the  drive immediately  goes to  the  BUS  FREE
       phase.     The   sense   data   is   set   to   ABORTED
       COMMAND/INITIATOR      DETECTED      ERROR      MESSAGE
       RECEIVED(0Bh/48h).   This error  does not  prevent  the
       initiator from retrying the command.

       If the  initiator sends  an  initiator  detected  error
       message immediately  after the COMMAND COMPLETE message
       is sent,  the   drive immediately  goes to the BUS FREE
       phase.     The  sense   data     is  set   to   ABORTED
       COMMAND/INITIATOR      DETECTED      ERROR      MESSAGE
       RECEIVED(0Bh/48h).   This error  does not  prevent  the
       initiator from retrying the command.


6.7.5     REJECTED Message

       When the  drive receives  a MESSAGE REJECT message from
       the initiator, it resends the original message.  If the






Doc 1014995, Rev B           18           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       message is  rejected again,  the drive takes one of the
       following actions, based on which message was rejected:

         COMMAND COMPLETE  - If  the rejected  message  is  a
          COMMAND COMPLETE message, the disk drive goes to the
          BUS FREE phase and does not consider this an error.

         DISCONNECT - If the rejected message is a DISCONNECT
          message, the  drive does  not  disconnect  from  the
          initiator and  continues the  current command.  This
          condition  does   not  preclude   the   drive   from
          attempting to disconnect at a later time.

          NOTE:     The  drive  does  not  send  a  DISCONNECT
          message to  an initiator  which does not support the
          disconnect/reconnect option.

         IDENTIFY (Reconnect) - If the rejected message is an
          IDENTIFY message,  the drive immediately goes to the
          BUS FREE  phase and aborts the current SCSI command.
          No further  reconnection is attempted, and no STATUS
          or COMMAND COMPLETE message is sent for the command.
          The sense  data is  set  to  HARDWARE  ERROR/MESSAGE
          ERROR(04h/43h).

         LINKED COMMAND COMPLETE - If the rejected message is
          a  LINKED   COMMAND  COMPLETE   message,  the  drive
          immediately goes  to the BUS FREE phase and does not
          read the next command in the linked list.  The sense
          data    is    set    to    HARDWARE    ERROR/MESSAGE
          ERROR(04h/43h).

         MESSAGE REJECT  -  If  the  rejected  message  is  a
          MESSAGE  REJECT   message,  the   drive  immediately
          terminates  the   present  command   with  a   CHECK
          CONDITION status and sets the sense data to HARDWARE
          ERROR/ MESSAGE ERROR (04h/43h).

         RESTORE  POINTERS   -  Since  the  RESTORE  POINTERS
          message is  only used  in an error recovery or retry
          situation, if  the rejected  message  is  a  RESTORE
          POINTERS message,  the drive  aborts the recovery or
          retry attempt,  assumes the  error is unrecoverable,
          and completes  the command  according to  the  error
          condition.

         SAVE DATA  POINTER - The drive assumes the initiator
          does not  support this  message and does not attempt
          to disconnect from the bus during this command.








Doc 1014995, Rev B           19           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


6.7.6     Initiator MESSAGE PARITY ERROR

       When the  drive receives a MESSAGE PARITY ERROR message
       from  the   initiator,  it  retries  the  operation  by
       resending the  original message.  If the message cannot
       be sent successfully, the drive immediately goes to the
       BUS FREE phase and aborts the current SCSI command.  No
       further reconnection  is attempted  and  no  STATUS  or
       COMMAND COMPLETE  message is  returned for the command.
       The sense  data is  set to  ABORTED COMMAND/SCSI PARITY
       ERROR (0Bh/47h).

6.7.7     RESELECTION Time-Out

       When the  drive attempts  to reselect the initiator and
       the initiator does not respond within a selection time-
       out delay  (as  defined  in  the  SCSI  standard),  the
       reselection is  aborted.    The    drive  attempts  the
       reselection 254  more times  and, if all attempts fail,
       the drive  aborts the current SCSI command.  No further
       reconnection is  attempted, and  no STATUS  or  COMMAND
       COMPLETE message  is returned  for the  command.    The
       sense data   is  set to  HARDWARE ERROR/SELECT/RESELECT
       FAILURE (04h/45h).

       NOTE: The initiator must have an overall  command time-
       out delay to detect this error.


6.7.8     Internal Controller Errors

       If an  error occurs within the embedded controller that
       is related  to the SCSI hardware or firmware, the drive
       terminates the  present command  with a CHECK CONDITION
       status  and   sets  the   sense  data     to   HARDWARE
       ERROR/INTERANALTARGET FAILURE  (04h/44h).   This  error
       does  not  prevent  the  initiator  from  retrying  the
       command.


















Doc 1014995, Rev B           20           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
    XT-4000S Product Specification & OEM Technical Manual

























































Doc 1014995, Rev B           61           Maxtor Corporation
Doc 1014995, Rev B           61           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


7.0  SCSI COMMAND DESCRIPTIONS

       This chapter describes the SCSI commands implemented by
       the Maxtor  XT-4000S Family  disk drives.   The command
       descriptions are  listed alphabetically  as a reference
       aid.   The SCSI Command Overview explains the fields in
       the command  descriptor block  (CDB) that are common to
       all commands.    Each  individual  command  description
       explains the  command function,  the CDB,  and any data
       returned.


7.1  SCSI COMMAND OVERVIEW

       This section  describes the fields in the CDB common to
       every command.   Each  SCSI command  is described  in a
       separate subsection, including CDB formats, hexadecimal
       operation  code,   byte  and  bit  functions,  and  any
       necessary effects produced by the commands.
       A request  from the initiator is performed by sending a
       CDB to  the drive.   For  some commands, the request is
       accompanied  by   a  list   of  parameters,   or  other
       information sent  during the  DATA OUT phase, or a list
       may be  returned to the initiator from the drive during
       the DATA  IN phase.   Table 71, Typical CDB for 6-Byte
       Commands,  and  Table  72,  Typical  CDB  for  10-Byte
       Commands,  show   the  basic   organization  of   CDBs.
       Explanations of those fields which are common among all
       commands follow.




                          Table 71
               Typical CDB for 6-Byte Commands





                          Table 72
               Typical CDB for 10-Byte Commands


       The reserved  bits, bytes,  fields, and code values are
       set aside  for future  standardization.   All  reserved
       bits, bytes,  or fields  are checked  by the  drive and
       must be set to zero.  If a reserved field is not set to
       zero, the  drive terminates  the command  with a  CHECK
       CONDITION status.   The  sense data  is set  to ILLEGAL






Doc 1014995, Rev B           62           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       REQUEST/INVALID FIELD  IN  CDB  (05h/24h),  or  ILLEGAL
       REQUEST/PARAMETER NOT SUPPORTED (05h/26h).

       The operation  code is  the first  byte of  a CDB  (see
       Table 73,  CDB Operation  Code Format).  The operation
       code contains  two fields:  the group code in the high-
       order three  bits, bits  five through  seven,  and  the
       command code  in the  low-order five  bits,  bits  zero
       through four.   The  group code specifies the length of
       the CDB and, together with the command code, determines
       the operation  to  be  performed.    If  the  specified
       operation code is invalid or not implemented, the drive
       returns a  CHECK CONDITION  status.   The sense data is
       set to  ILLEGAL REQUEST/INVALID  COMMAND OPERATION CODE
       (05h/20h).




                          Table 73
                  CDB Operation Code Format


       The group code specifies one of the following groups:

          Group 0   - 6-byte commands (see Table 71).
          Group 1 & 7    - 10-byte commands (see Table 72).

       The command code specifies one of the commands in Table
       74, CDB Operation Codes.




                          Table 74
                     CDB Operation Codes


       The logical unit number (LUN) field contains the number
       of the  device being addressed.  The drive, acting as a
       SCSI bus  target, supports  only a  LUN field  value of
       zero.   Therefore, the value for the LUN field (in byte
       one of  the CDB)  is limited  to 000  (binary).   If an
       invalid LUN field value is specified, the drive returns
       a CHECK  CONDITION status.   The  sense data  is set to
       ILLEGAL  REQUEST/UNSUPPORTED  LOGICAL  UNIT  (05h/25h).
       The drive provides this method of addressing the device
       for initiators  that  do  not  implement  the  IDENTIFY
       message.   An LUN  specified in  the  IDENTIFY  message
       overrides any LUN specified in the CDB.







Doc 1014995, Rev B           63           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       The relative  address (RelAdr)  bit is  set to  one  to
       indicate that  the LBA  portion of  the CDB  is a  twos
       complement displacement.   This  negative  or  positive
       displacement is  added to  the LBA last accessed on the
       logical unit,  to form  the LBA for this command.  This
       feature is only available when linking commands, and it
       requires that  a previous  command in  the linked group
       have accessed a block of data on the logical unit.

       The LBA  field begins with block zero and is contiguous
       up to  the last  logical block.   The  maximum  LBA  is
       variable, depending  on the parameters selected for the
       number of  bytes per  sector and  number  of  alternate
       sectors.

       NOTE: The maximum  LBA allowable  is returned to a READ
       CAPACITY command  with a  partial media indicator (PMI)
       bit equal to zero.

       Group 0  commands contain  21-bit LBAs.   Group 1 and 7
       commands contain 32-bit LBAs.

       The control  byte is  the last  byte in every CDB.  The
       control byte  is separated  into three fields, as shown
       in Table 75, Control Byte.



                          Table 75
                         Control Byte


       Bits seven through two are reserved.

       Bit one is defined as the flag bit, and is only checked
       when the  link bit is set to one.  When the flag bit is
       zero, the drive sends a LINKED COMMAND COMPLETE message
       when the  command completes  successfully.  If the flag
       bit is  set to  one, the  drive sends  a LINKED COMMAND
       COMPLETE (WITH FLAG) message when the command completes
       successfully.

       Bit zero  is defined as the link bit.  When the current
       command completes  successfully and the link bit is set
       to one,  the  drive  returns  an  INTERMEDIATE  status,
       followed by one of the two messages defined by the flag
       bit above.   The  drive then automatically links to the
       next command.   If  a linked  command is  not completed
       successfully,  the  drive  returns  a  CHECK  CONDITION
       status, and does not link to the next command.






Doc 1014995, Rev B           64           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       The remaining  bytes in  the CDB  are primarily command
       dependent,  and   are  described   in   the   following
       individual command sections.





















































Doc 1014995, Rev B           65           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
FORMAT UNIT
    XT-4000S Product Specification & OEM Technical Manual
                                                   FORMAT UNIT


7.2  FORMAT UNIT

       The FORMAT  UNIT command  ensures that  the  medium  is
       formatted so that all data blocks can be accessed.  The
       drive maintains  a defective  sector and  track file on
       the disk  on a  cylinder that  is not accessible to the
       initiator.     During  the   formatting  process,   the
       initiator may  specify a  set of  defective  blocks  or
       tracks to be reassigned using spare blocks or alternate
       tracks, as appropriate.

       The FORMAT  UNIT command  requires two disk revolutions
       to format each track.  When certification is enabled, a
       minimum of  four revolutions is required to format each
       track.

       The FORMAT  UNIT command  uses four  different sets  of
       defect information:

         Primary, or  Manufacturer's, Defect  List (P list) -
          The  primary   defect  list   is  supplied   by  the
          manufacturer, and is stored on the disk.

         Certification Defect  List (C  list or Certification
          Process) -  The certification  defect list  includes
          the defects  detected by  the drive  during a verify
          operation  of   the  FORMAT   UNIT  command.     The
          certification defects are added to the grown list (G
          list) by the drive.  During the FORMAT UNIT command,
          if the  format data (FmtData) bit is one, the format
          options valid  (FOV) header  bit equals one, and the
          disable certification (DCRT) header bit equals zero,
          the drive  automatically develops  the certification
          defect list  and maps  out the defects from the user
          accessible area of the disk.

         Initiator Defect  List  (D  list)  -  The  initiator
          defect  list   is  supplied  to  the  drive  by  the
          initiator in  the DATA  OUT  phase.    The  list  is
          supplied by  the initiator  when the  FmtData bit is
          one, and  the defect  list length of the defect list
          header is  greater than  zero.   If the  defect list
          length  is   zero,  no   defect  descriptor(s)   are
          transferred.     The  defects   identified  by   the
          initiator in  the D list are mapped out and added to
          the grown  list (G list).  The initiator defect list
          is added  to the  G list.   The  drive automatically
          maps out the defects from the user accessible area.






Doc 1014995, Rev B           66           Maxtor Corporation
Doc 1014995, Rev B           66           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
                                                   FORMAT UNIT

         Grown Defect  List (G  list) -  This  list  includes
          defects identified  to, or  by, the drive (the C, D,
          and G  lists).   It does  not include  the  P  list.
          These defects  are  classified  as  flaws  appearing
          after the  media have been formatted.  The initiator
          may request  that the  current G list be used during
          formatting by setting CmpLst to zero, and FmtData to
          one, or  that the current G list be erased and a new
          one begun  by setting  CmpLst to one, and FmtData to
          one).   Entries  to  this  G  list  include  defects
          provided to  the drive  in D  lists during  previous
          FORMAT UNIT  commands,  the  drive  C  list  defects
          detected during  the previous  FORMAT UNIT  command,
          and defects appended by successful completion of the
          REASSIGN BLOCKS command.

               NOTE:     If  a  P  list  defect  is  near  the
          boundary of  two sectors,  the G list may contain an
          entry after  formatting, even  though the  initiator
          did not  supply a  D list  or enable  certification.
          This additional  entry  indicates  that  the  second
          sector was  reassigned to  prevent a known defect in
          the first  sector from affecting data in the second.
          If the  new entry  in the  G list  shows a length of
          FFFFFFFFh, the track was reassigned due to a lack of
          alternate sectors.


7.2.1     Defect List Management

       The FORMAT  UNIT command  uses the  drive geometry, and
       format information  read from  a reserved  area on  the
       disk during  power up,  to format  the  media.    These
       parameters may  be changed  by using  the  MODE  SELECT
       command prior  to issuing  the FORMAT UNIT command.  If
       the information  contained  in  the  reserved  area  is
       invalid, or  cannot be  read, the  FORMAT UNIT  command
       uses the  default parameters,  as returned  by  a  MODE
       SENSE command.   See  7.5  MODE  SENSE  later  in  this
       chapter.

       In order  for any  list of defects to be relocated, the
       drive's current  values for  the  alternates  per  zone
       field in  MODE SELECT, Page Code 3, or MODE SENSE, Page
       Code 3, must be greater than zero.

       The initiator may select how the drive handles the list
       by using  bits in  the CDB  and the  defect list header
       (see Table 76, FORMAT UNIT CDB).

       The drive  has the  capability of mapping out defective
       sectors so  that the  media appears  error free  to the





Doc 1014995, Rev B           67           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
FORMAT UNIT

       initiator.    The initiator may use the disable primary
       (DPRY), and format options valid (FOV), bits to request
       the drive  to relocate  the P  list recorded  by Maxtor
       prior to  shipment.  The drive maintains, and maps out,
       an additional list of flaws (G list) on the disk unless
       requested not  to by  the initiator  in the FORMAT UNIT
       CDB, by  setting the complete list (CmpLst) bit.  The G
       list, if  it exists  and is  readable, may  include any
       errors identified  by  the  initiator  in  the  D  list
       supplied in  the defect descriptors during the DATA OUT
       phase of  the FORMAT UNIT command.  The G list may also
       include any  errors identified by the drive (C list) by
       using the  disable  certification  (DCRT),  and  format
       options valid  (FOV), bits  in the D list header during
       the DATA  OUT phase  of a  FORMAT UNIT  command.  The G
       list also  includes errors previously identified by all
       REASSIGN BLOCK commands that have been issued since the
       last completion  of a  FORMAT  UNIT  command  with  the
       complete list (CmpLst) bit set to one.

       With the  MODE SELECT  command, the initiator specifies
       how many  sectors are  deallocated, either per track or
       per cylinder,  to handle  bad sectors.   See  the  zone
       definition  in   7.5.6  Direct-Access   Device   Format
       Parameters  Page   later  in  this  chapter.    If  the
       initiator deallocates  no spare  sectors with  the MODE
       SELECT command  (zero alternates  per zone),  then  the
       drive does  not map  out any  flaws or create any spare
       sectors (the initiator operating system must handle the
       defects).   If the initiator attempts either a REASSIGN
       BLOCK ,  or FORMAT  UNIT, command  which involves block
       reassignment, without first deallocating spare sectors,
       the drive returns an error condition.

       The initiator  may disable the relocation of all defect
       lists (including  default format)  while  enabling  the
       deallocation of  spare sectors  (assuming  the  current
       value of  alternates per zone is greater than zero), by
       performing a  FORMAT UNIT  command 04,  18, 00, 00, 00,
       00, with a header DATA OUT phase of 00, E0 (or F0), 00,
       00.

       The  initiator   may  disable   deallocation  of  spare
       sectors,  and   relocation  of  all  defect  lists,  by
       performing a MODE SELECT command, which sets alternates
       per zone,  and alternates per volume, to zero, followed
       by a FORMAT UNIT command 04, 00, 00, 00, 00, 00.










Doc 1014995, Rev B           68           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
                                                   FORMAT UNIT

7.2.2     SCSI Deviations

       The vendor  unique byte in the CDB is used to specify a
       1 byte  data pattern,  to be written in the sector data
       area during  the format  operation, if certification is
       disabled (disable certification+DCRT+bit equals zero).


7.2.3     Command Parameters

       The CDB  for the  FORMAT UNIT  command is  formatted as
       shown in Table 76, FORMAT UNIT CDB.




                          Table 76
                       FORMAT UNIT CDB


       A format  data (FmtData)  bit of  one indicates  that a
       DATA OUT  phase takes  place during  command execution.
       The DATA  OUT phase  consists of the 4 byte defect list
       header and, if there is a nonzero defect list length, a
       D list.   The  header specifies  if the  drive  formats
       using the  P list  and/or C list, if the drive stops on
       an error  during format,  and the length of the D list,
       if any.   The optional D list follows the header during
       the DATA OUT phase.  The D list consists of one or more
       defect descriptors.   The  format  of  the  D  list  is
       determined by  the defect  list format  defined by bits
       zero through two of the CDB.

       A format  data (FmtData) bit of zero indicates that the
       DATA OUT  phase does  not occur  (no defect list header
       and  no   defect  descriptors   are  supplied   by  the
       initiator).  If MODE SELECT Page Code 3 (alternates per
       zone) does  not equal  zero, then  the P list and the G
       list (if  one exits) are mapped out.  If alternates per
       zone equals  zero, then  no defects  are mapped out and
       the drive  is not  requested to  handle defects at all.
       No  spare  locations  are  deallocated  by  the  drive.
       Further REASSIGN  BLOCK commands  are rejected  with  a
       CHECK CONDITION status and ILLEGAL REQUEST sense key.

       A complete  list (CmpLst)  bit of  one indicates  the D
       list defined by the initiator during the DATA OUT phase
       of the  command execution is the complete list of known
       defects.  The result is to erase the current G list and
       build a new G list.







Doc 1014995, Rev B           69           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
FORMAT UNIT

       NOTE: The format  data (FmtData)  bit must equal one if
       the complete list (CmpLst) bit equals one.

       A complete list (CmpLst) bit of zero indicates that the
       data supplied  by the  initiator during  the  DATA  OUT
       phase (header  only, or  header and  descriptors) is an
       addition to  existing defect  data already removed from
       the initiator-addressable  blocks.   The result is that
       the existing  G list  (if one  exists) is used.  At the
       initiator request,  the P,  C, and/or  D lists are also
       used.

       The defect list format is used to specify the format of
       the defect  descriptors used  for a  D list.  See 7.2.5
       Initiator Defect List later in this chapter.

       The  format  data  pattern  field  specifies  the  byte
       pattern to  be written  in the data area when the drive
       is formatted.   A value of zero in this field specifies
       that the  drive should  use the default pattern of E5h,
       if CERTIFY is disabled.

       The interleave field specifies the interleave factor to
       be used  for this  format operation.   The drive checks
       the most significant byte of the interleave field (byte
       three) for  a zero.  An interleave value of zero or one
       requests that  the target  use its  default  interleave
       (1:1 sequential).

       NOTE: It is  recommended that  an interleave  of 1:1 be
       used  in   all  cases.     Any   other  value  degrades
       performance.


7.2.4     Format Modes

       The format  mode is  selected by  a combination  of the
       FORMAT UNIT  CDB, and  the defect list header.  Through
       control  of   the  appropriate  fields,  the  initiator
       determines whether  the drive's  internal defect  lists
       are used,  the initiator  is to supply the defect list,
       or both.   The  D list  is discussed in detail in 7.2.5
       Initiator Defect List later in this chapter.

       If the  format data  (FmtData) bit  is set  to one, the
       drive  transfers   the  defect  list  header  from  the
       initiator to the drive during the DATA OUT phase of the
       FORMAT UNIT command.  The defect list header is 4 bytes
       long, followed by zero or more defect descriptors.  The
       header specifies  the total  number  of  bytes  in  the
       defect list  and several parameters for the format mode
       (see Table 77, FORMAT UNIT Defect List Header).





Doc 1014995, Rev B           70           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
                                                   FORMAT UNIT



                          Table 77
                FORMAT UNIT Defect List Header


       A format  options valid (FOV) bit of one indicates that
       the other  fields in this byte are valid and may be set
       to one  also.   If this  bit is  set to  zero, bits one
       through six  must also  be set  to zero,  and the drive
       formats the disk drive using the P list.

       A disable  primary (DPRY) bit of one specifies that the
       drive is  to format the media without using the P list.
       If this  bit is  zero, the drive uses the P list.  This
       bit is only valid if the format options valid (FOV) bit
       is set to one.

       A disable  certification (DCRT)  bit of  one  indicates
       that the  drive enables the certification routine while
       formatting.   When set  to one,  the bit indicates that
       the drive  disables  the  certification  routine  while
       formatting.   This bit  is only  valid  if  the  format
       options valid (FOV) bit is set to one.

       A stop  format (STPF)  bit of  one specifies  that  the
       drive terminates  the command  when  it  encounters  an
       unrecoverable error  while accessing  any of the defect
       lists.   When this bit is zero, the drive continues the
       format operation  if any  of the  above  errors  occur.
       This bit  is only  valid if  the format  options  valid
       (FOV) bit is set to one.

       The initialization  pattern option allows the initiator
       to initialize  the initiator  accessible areas  of  the
       media to a specified pattern.  The pattern is specified
       in the  initialization pattern descriptor output during
       the DATA OUT phase.

       The initialization  pattern is  not intended  for media
       analysis or certification. It is used to initialize the
       data in  the initiator  accessible area of the media to
       the specified pattern.

       An initialization  pattern (IP)  bit of  one  indicates
       that an  initialization pattern  descriptor is supplied
       during the  DATA OUT  phase, immediately  following the
       defect list  header.   An IP bit of zero indicates that
       no  initialization  pattern  descriptor  will  be  sent
       during the  DATA OUT  phase.  If the IP bit is zero the
       drive will  use its default initialization pattern when





Doc 1014995, Rev B           71           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
FORMAT UNIT

       it formats  the disk.  See Table 78 for Initialization
       Pattern Descriptor.




                          Table 78
              Initialization Pattern Descriptor


       The IP  modifier field  specifies the type and location
       of a  header that  modifies the initialization pattern.
       The IP modifier is defined in Table 79.

       The initialization  pattern type  field  indicates  the
       type of  pattern the  drive will use to initialize each
       logical block  within the  initiator accessible portion
       of the  media.   The  initialization  pattern  type  is
       defined in  Table 710.   All  bytes within  a  logical
       block are written with the initialization pattern.  The
       initialization  pattern  may  be  modified  by  the  IP
       modifier field as described above in Table 79.




                          Table 79
               Initialization Pattern Modifier





                          Table 710
                 Initialization Pattern Type


       The initialization  pattern length  field indicates the
       number  of   bytes  contained   in  the  initialization
       pattern.   If the  length exceeds  the current  logical
       block size,  the drive  returns CHECK CONDITION status.
       The sense  data is set to ILLEGAL REQUEST/INVALID FIELD
       IN PARAMETER  LIST.  The pattern may be modified by the
       IP modifier field.

       The  disable   saving  parameters   (DSP)  bit  is  not
       supported by the drive and must be set to zero.

       An immediate  (Immed) bit  of zero  specifies that  the
       drive return  status after  the  format  operation  has
       completed.   An Immed  bit of  one specifies  that  the






Doc 1014995, Rev B           72           Maxtor Corporation
    XT-4000S Product Specification & OEM Technical Manual
                                                   FORMAT UNIT

       drive return  status as  soon as the command descriptor
       block has  been validated,  and the  entire defect list
       has been  transferred.  If the  Immed bit is one during
       the  format   operation,  the  drive  will  respond  as
       follows:

              In response  to  all  commands  except  REQUEST
           SENSE and  INQUIRY, the  drive  will  return  CHECK
           CONDITION status.

              In response  to the  INQUIRY command, the drive
           will return the INQUIRY data.

              In  response  to  the  REQUEST  SENSE  command,
           unless an error has occurred, the drive will return
           a sense  data of  NOT READY/LOGICAL  UNIT NOT READY
           FORMAT IN  PROGRESS, with  the sense  key  specific
           bytes set for format progress indication.

       The vendor unique (VU) bit is reserved, and must be set
       to zero.

       The defect list length field specifies the total number
       of bytes  (not the  total number of defect descriptors)
       in the D list (provided by the initiator).  This length
       does not  include the  4 bytes in the header.  A defect
       list length  of  zero  indicates  that  no  D  list  is
       provided by  the initiator,  and is  not considered  an
       error by the disk drive.

       The format  mode for  the drive  is specified  with the
       following bits:   format  data (FmtData), complete list
       (CmpLst),   disable   primary   (DPRY),   and   disable
       certification (DCRT).   If  the  format  options  valid
       (FOV) bit  in the defect list header is zero, or if the
       format data (FmtData) bit is zero, the drive treats the
       disable primary (DPRY) and disable certification (DCRT)
       bits as if they were set to zero and one, respectively.
       Table 711,  FORMAT UNIT  Drive Format Modes, lists the
       format  modes   supported  by   the  drive,  and  their
       corresponding states for the 4 bits.




                          Table 711
                FORMAT UNIT Drive Format Modes










Doc 1014995, Rev B           73           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
FORMAT UNIT

7.2.5     Initiator Defect List

       In order  for the  initiator to  provide a  D list, the
       format data  (FmtData) bit  must be  set to  one in the
       CDB, and  bits zero  through two of byte one in the CDB
       must be  set to one of the three valid options shown in
       Table 712,  FORMAT UNIT  D List  Formats.   Also,  the
       defect list  length, bytes  two and three of the defect
       list header,  must be  set to  the appropriate  nonzero
       value.   The three  valid D  list options, block, bytes
       from index,  and physical,  are detailed  as  in  Table
       712.

       NOTE: The initiator  should use  the  drive's  internal
       defect maps, rather than sending a D list to the drive.
       Maxtor performs  extensive testing  of all  drives, and
       adds all  areas of defective or marginal performance to
       the defect  lists.    If  the  initiator  disables  the
       internal lists  using the  disable primary  (DPRY) bit,
       marginal sectors  might  cause  future  loss  of  data.
       Also,  the   drive  uses  sophisticated  algorithms  to
       determine when  to deallocate  multiple sectors  for  a
       single defect.  The limitations of the bytes from index
       format of  the  READ  DEFECT  LIST  and    FORMAT  UNIT
       commands do  not allow  for reporting  the length  of a
       defect, even though this information is stored in the P
       list.   Therefore, the  drive is  better able  to judge
       when a  defect will cross sector boundaries than is the
       initiator.




                          Table 712
                  FORMAT UNIT D List Formats



A    D LIST BLOCK FORMAT

       The D  list is  transferred from  the initiator  to the
       drive during  the DATA  OUT phase  of the  FORMAT  UNIT
       command.

       NOTE: It is  recommended that  the bytes from index, or
       physical sector, defect list formats be used during the
       format operation.

       The D  list begins  with a  4 byte  header, followed by
       zero or  more 4  byte defect  descriptors.   When the D
       list is specified using block addresses, the disk drive






Doc 1014995, Rev B           74           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
                                                   FORMAT UNIT

       uses the  following format  described  in  Table  713,
       FORMAT UNIT Defect Descriptor(s), Block Format.



                          Table 713
        FORMAT UNIT Defect Descriptor(s), Block Format


       The D  list LBA  field specifies  the  address  of  the
       logical block  that contains  the defect.  The location
       of the blocks in the D list refers to the current block
       length and block addresses.

       Each  defect  descriptor  for  the  block  format  mode
       specifies a 4 byte defect LBA that contains the defect.
       The defect descriptors must be in ascending order.


B    D LIST BYTES FROM INDEX FORMAT

       The D  list is  transferred from  the initiator  to the
       drive during  the DATA  OUT phase  of the  FORMAT  UNIT
       command.   The D  list begins  with a  4  byte  header,
       followed by  zero or  more 8  byte defect  descriptors.
       When the  D list is specified using the number of bytes
       from index,  the drive  uses the  format  described  in
       Table 714,  FORMAT UNIT  Defect  Descriptor(s),  Bytes
       from Index Format.




                          Table 714
  FORMAT UNIT Defect Descriptor(s), Bytes from Index Format


       The cylinder  number  of  defect  field  specifies  the
       physical cylinder number which contains the defect.

       The head  number of  defect field  specifies  the  head
       number which contains the defect.

       The defect  bytes from index field specifies the number
       of bytes  between the  index  and  the  defect  on  the
       specified track.   A  value of  FFFFFFFFh in  the bytes
       from index  field indicates that the entire track is to
       be reassigned.








Doc 1014995, Rev B           75           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
FORMAT UNIT

       The defect descriptors must be in ascending order.  For
       determining ascending  order, the  cylinder  number  of
       defect is  considered the  most significant part of the
       address, and  the defect bytes from index is considered
       the least significant part of the address.


C    D LIST PHYSICAL SECTOR FORMAT
       The defect  list is  transferred from  the initiator to
       the drive  during the DATA OUT phase of the FORMAT UNIT
       command.   The defect list begins with a 4 byte header,
       followed by  zero or  more 8  byte defect  descriptors.
       When the defect list is specified using physical sector
       addresses, the  drive uses  the format  in Table  715,
       FORMAT  UNIT   Defect  Descriptor(s),  Physical  Sector
       Format.




                          Table 715
   FORMAT UNIT Defect Descriptor(s), Physical Sector Format


       The cylinder  number  of  defect  field  specifies  the
       physical cylinder number which contains the defect.

       The head  number of  defect field  specifies  the  head
       number which contains the defect.

       The defect  sector number  field specifies  the  sector
       number which contains the defect.  A value of FFFFFFFFh
       in the  defect sector  number field  indicates that the
       entire track is to be reassigned.

       The defect descriptors must be in ascending order.  For
       determining ascending  order, the  cylinder  number  of
       defect is  considered the  most significant part of the
       address, and the defect sector number is considered the
       least significant part of the address.


7.2.6     Error Conditions

       If the  interleave value  exceeds the maximum number of
       sectors per  track, the  drive terminates  the  command
       with a  CHECK CONDITION  status and sets the sense data
       to ILLEGAL REQUEST/INVALID FIELD IN CDB (05h/24h).

       If the format mode is invalid, the drive terminates the
       command with  a CHECK  CONDITION status  and  sets  the





Doc 1014995, Rev B           76           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
                                                   FORMAT UNIT

       sense data  to ILLEGAL  REQUEST/INVALID  FIELD  IN  CDB
       (05h/24h),  or   ILLEGAL   REQUEST/INVALID   FIELD   IN
       PARAMETER LIST (05h/26h), whichever is applicable.

       If the  stop format  (STPF) bit  is one,  and the drive
       encounters an  unrecoverable error reading or accessing
       a defect  list, the drive terminates the command with a
       CHECK CONDITION  status and  sets  the  sense  data  to
       MEDIUM ERROR/DEFECT LIST ERROR (03h/19h).

       If the  drive has insufficient capacity to reassign all
       the defective  blocks, it terminates the command with a
       CHECK CONDITION  status and  sets  the  sense  data  to
       MEDIUM ERROR/DEFECT LIST UPDATE FAILURE (03h/32h).

       If the  stop format  (STPF) bit  is zero, and the drive
       encounters an  error while  accessing a defect list, it
       continues the FORMAT UNIT command.  When the command is
       completed, and  no other  errors occur,  it  terminates
       with a  CHECK CONDITION  status and  and sets the sense
       data to RECOVERED ERROR/DEFECT LIST ERROR (01h/19h).

       If the  format options  valid (FOV)  bit in  the defect
       list header  is zero,  and the  disable primary (DPRY),
       disable certification  (DCRT), and  stop format (STPF),
       bits are  not zero,  the drive  terminates the  command
       with a  CHECK CONDITION  status.  The sense data is set
       to ILLEGAL  REQUEST/INVALID  FIELD  IN  PARAMETER  LIST
       (05h/26h).

       If the  stop format  (STPF) bit  is  one,  the  disable
       primary (DPRY) bit is zero, and the drive cannot locate
       the P  list, the  drive terminates  the command  with a
       CHECK CONDITION  status and  sets  the  sense  data  to
       ILLEGAL REQUEST/DEFECT LIST NOT FOUND (05h/1Ch).

       If the  stop format  (STPF) bit  is zero,  the  disable
       primary (DPRY) bit is zero, and the drive cannot locate
       the P list, it continues the FORMAT UNIT command.  When
       the command  is completed,  and no  other errors occur,
       the drive  terminates with a CHECK CONDITION status and
       sets the  sense data to a RECOVERABLE ERROR/DEFECT LIST
       NOT FOUND   (01h/1Ch) .

       If  the   drive  does   not  have  valid  data  in  the
       configuration cylinder  or a  FORMAT UNIT  command  was
       interrupted by  a RESET,  the drive  terminates with  a
       CHECK CONDITION  status and   sets  the sense  data  to
       MEDIUM ERROR/MEDIUM FORMAT CORRUPTED (03h/31h).








Doc 1014995, Rev B           77           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
INQUIRY
    XT-4000S Product Specification & OEM Technical Manual
                                                       INQUIRY


7.3  INQUIRY

       The INQUIRY  command provides  a  means  by  which  the
       initiator may request information regarding the drive.

       If an  INQUIRY command  is received  from an  initiator
       with a  pending UNIT  ATTENTION  condition,  the  drive
       executes the  INQUIRY command,  returns a  GOOD status,
       and does not clear the UNIT ATTENTION condition.

       When the  INQUIRY command  is sent to a nonexistent LUN
       (i.e., any  LUN other  than zero),  the drive transfers
       the INQUIRY  response data  back to  the initiator  and
       terminates the command with GOOD status.  The initiator
       must  examine  the  peripheral  device  type  field  to
       determine if it is a valid LUN.


7.3.1     SCSI Deviations

       There are no deviations.


7.3.2     Command Parameters

       The INQUIRY  CDB is  formatted as  shown in Table 716,
       INQUIRY CDB.




                          Table 716
                         INQUIRY CDB


       The  enable  vital  product  data  (EVPD)  bit  is  not
       supported by the drive and must be set to zero.

       The page  code field  is not supported by the drive and
       must be set to zero.

       The allocation  length field  specifies the  number  of
       bytes the  initiator has  allocated  for  the  returned
       INQUIRY data.   An  allocation length of zero indicates
       that no  data is transferred to the initiator, and this
       is not  considered an error.  Any other value indicates
       the maximum  number of bytes that are transferred.  The
       drive terminates  the data  transfer when the number of
       bytes specified  in  the  allocation  length  field  is

    XT-4000S Product Specification & OEM Technical Manual
                                                       INQUIRY

       transferred, or  when all  available  INQUIRY  data  is
       transferred, whichever is less.


7.3.3     Data Format

       The INQUIRY  command returns  36 bytes  of data  to the
       initiator.   This data  is formatted  as in Table 717,
       INQUIRY Response Data.




                          Table 717
                    INQUIRY Response Data


       The peripheral  qualifier and  peripheral  device  type
       fields  identify  the  device  characteristics  of  the
       logical unit.    If the logical unit number is zero the
       peripheral qualifier  is 000b and the peripheral device
       type is  00000b.   This indicates  that the  device  is
       currently connected as logical unit zero and that it is
       a direct-access device.

       If the  logical unit number is not zero, the peripheral
       qualifier is  011b and  the peripheral  device type  is
       11111b.   This indicates  that the  logical unit is not
       supported and the peripheral device type is unknown.

       The removable medium bit (RMB) is zero since the medium
       is not removable.

       The ISO  version field  is zero  because the drive does
       not claim compliance to the ISO version of SCSI (ISO IS
       9316).

       The ECMA version field is zero since the drive does not
       claim compliance  to the  ECMA version  of SCSI  (ECMA-
       111).

       The ANSI-approved version field is 001b to indicate the
       drive claims  compliance with  the ANSI version of SCSI
       (X3.131-1986).

       The asynchronous  event notification  capability (AENC)
       bit is not supported by the drive and is zero.

       The terminate I/O process (TrmIOP) bit is not supported
       by the drive and is zero.

    XT-4000S Product Specification & OEM Technical Manual
INQUIRY

       The response data format is 1h to indicate the drive is
       compatible  with   the   Common   Command   Set   (CCS)
       requirements.

       The additional  length field  indicates the  length  in
       bytes of  the remaining  data to  be returned.   If the
       allocation length  of the  command descriptor  block is
       too small  to  transfer  all  of  the  parameters,  the
       additional length  is   not  adjusted  to  reflect  the
       truncation.

       The relative addressing (RelAdr) bit is one to indicate
       that the drive supports the relative addressing mode.

       The wide  bus 32  (WBus32) bit  is not supported by the
       drive and is zero.

       The wide  bus 16  (WBus16) bit  is not supported by the
       drive and is zero.

       The synchronous  transfer (Sync) bit is one to indicate
       that the drive supports synchronous data transfer.

       The linked command (Linked) bit is one to indicate that
       the drive supports linked commands.

       The command  queuing (CmdQue)  bit is  not supported by
       the drive and is zero.

       The soft reset (SftRe) bit is zero to indicate that the
       drive supports the hard RESET alternative.

       ASCII data  fields shall  contain  only  graphic  codes
       (i.e., code  values 20h  through  7Eh).    Left-aligned
       fields shall  place any  unused bytes at the end of the
       field (highest  offset) and  the unused  bytes shall be
       filled with  space  characters  (20h).    Right-aligned
       fields shall place any unused bytes at the start of the
       field (lowest  offset) and  the unused  bytes shall  be
       filled with space characters (20h).

       The vendor identification field contains eight bytes of
       ASCII data  identifying MAXTOR  as the  vendor  of  the
       product.  The data is left aligned within this field.

       The product identification field contains sixteen bytes
       of ASCII  data as  defined by  the vendor.  The data is
       left-aligned within  this field.  The following product
       identifications are returned:

              The XT-4170S drive returns "XT-4170S________"
              The XT-4380S drive returns "XT-4380S________"

    XT-4000S Product Specification & OEM Technical Manual
                                                       INQUIRY

              Prior to becoming ready the the XT-4000S drives
       return "XT-4000S________"

       The product revision level field contains four bytes of
       ASCII data  that indicate  the firmware revision level.
       The data is left-aligned within this field.

       NOTE: Products that  incorporate an  EEPROM will report
       the correct  model number  before spinning up to READY,
       as well as after.

       The revision  level field  contains the Maxtor firmware
       revision level  in ASCII.  There are four characters in
       the string.

    XT-4000S Product Specification & OEM Technical Manual
MODE SELECT
    XT-4000S Product Specification & OEM Technical Manual
                                                   MODE SELECT


7.4  MODE SELECT

       The MODE  SELECT command  provides a means by which the
       initiator may  specify various parameters to the drive.
       Any changes  in the  mode parameters  take effect  upon
       successful completion  of the MODE SELECT command.  The
       MODE SELECT  command is complementary to the MODE SENSE
       command, which  allows the  initiator  to  request  the
       values of the mode parameters from the drive.

       The initiator  can send  the drive  optional blocks  of
       parameters  that   are  separated   into  pages.    The
       individual pages  specify mode parameters which control
       the configuration and performance of the drive.

       The mode  parameter pages  3 and  4 are  written to the
       medium  when  the  FORMAT  UNIT  command  is  executed.
       Subsequent drive power up or reset conditions cause the
       drive to read this information from the medium.

       The initiator  sends those pages to the drive for which
       it requests  parameters to  be changed.   The initiator
       may send  pages individually, or all pages at one time,
       and the  pages do not need to be sent in any particular
       order.

       It is  recommended that, prior to issuing a MODE SELECT
       command,  the   initiator  first  issue  a  MODE  SENSE
       command, with  the page code set for all pages, and the
       page control field set for current values, to determine
       which pages  are implemented,  the  page  lengths,  and
       current values.   This  should be  followed by  another
       MODE SENSE  command, with the page control field set to
       changeable values,  to determine  which values  may  be
       altered.      The   initiator   should   analyze   this
       information, and should not issue a MODE SELECT command
       which attempts to change values in fields which are not
       implemented or not changeable.

       Following   a MODE  SELECT  command  that  changes  any
       parameters, the  drive returns a CHECK CONDITION status
       to the  first command  received  from  all  initiators,
       except the one that issued the MODE SELECT command. The
       sense data  is set  to UNIT  ATTENTION/MODE  PARAMETERS
       CHANGED (06h/2Ah).   When  a  MODE  SELECT  command  is
       issued that  changes any  parameters in  page 3 or 4, a
       FORMAT UNIT  command must  be issued  prior to the next
       media access  command.   If this  is not  done, current
       values for pages 3 and 4 are not saved, and physical to
       logical translations are incorrect for media access.

    XT-4000S Product Specification & OEM Technical Manual
                                                   MODE SELECT

       The MODE  SELECT command can affect the following types
       of drive parameters:

         Saved  Values:     The  saved  values  are  all  the
          changeable MODE SELECT parameters saved by the drive
          on the  medium.   The initiator may change the saved
          values of  pages 1  and 2  by issuing  a MODE SELECT
          command with  the save  parameters (SP)  bit set  to
          one.   This action  does not change the saved values
          of pages  3 and  4.   Only a FORMAT UNIT Command can
          change the saved values of  pages 3 and 4.

         Current Values:   The  current values  are the  MODE
          SELECT parameters  used by  the drive  during normal
          operation.   Any MODE  SELECT command issued changes
          the current values.


7.4.1     SCSI Deviations

       Only a  single block  descriptor may  be  sent  to  the
       drive.

       The number  of blocks  field in the block descriptor is
       ignored.

       MODE SELECT  data for  pages 1  and 2 (both current and
       saved values) are maintained separately for each of the
       seven possible  initiators.   This avoids the necessity
       of  reporting   an  UNIT  ATTENTION  condition  to  all
       initiators when  one initiator  has  changed  the  mode
       parameters.


7.4.2     Command Parameters

       The MODE  SELECT command descriptor block is defined in
       Table 718, MODE SELECT Command.



                          Table 718
                     MODE SELECT Command


       A page  format (PF)  bit of one indicates that the data
       sent by  the initiator,  after the header and the block
       descriptors (if any), is in page format.

       A save  parameters (SP)  bit of  one specifies that the
       drive should  take the current values and write them to

    XT-4000S Product Specification & OEM Technical Manual
MODE SELECT

       the medium as the saved values.  Before the drive saves
       the parameters,  it makes any changes to these pages as
       specified in  the current  MODE SELECT command.  If the
       drive  encounters  an  error  during  the  MODE  SELECT
       command, it  terminates the command without writing the
       parameters to  the medium  as the saved values.  If the
       save parameters (SP) bit is zero, the drive updates the
       current values  and does  not modify  the saved values.
       The SP  bit is  ignored for  pages 3  and 4,  which are
       always saved by a FORMAT UNIT command.

       The parameter  list length  field specifies the length,
       in bytes,  of the data that is sent from the initiator.
       A parameter  list length of zero indicates that no data
       is transferred  and is  not considered  an error by the
       drive.


7.4.3     Parameter List Format

       The MODE  SELECT data  is sent  by the initiator to the
       drive during the DATA OUT phase.  This data consists of
       a parameter list header, zero or one block descriptors,
       and zero  or more  page descriptors.  The entire length
       of the  data is  specified in  the MODE  SELECT command
       descriptot block.

       The parameter list header is 4 bytes, and specifies the
       medium type and the length of the block descriptor.

       The block descriptor consists of 8 bytes, and specifies
       the density  code, the  number of blocks, and the block
       length.

       The  page  descriptors  contain  the  mode  parameters,
       separated into  pages.   These mode  parameters control
       options and  features which  the initiator  may change.
       One or  more pages  may be  sent during the MODE SELECT
       command.


A    PARAMETER LIST HEADER FORMAT

       The MODE SELECT parameter list header is the first part
       of the  parameter list.   The  header is  formatted  as
       shown in Table 719, MODE SELECT Parameter List Header.

    XT-4000S Product Specification & OEM Technical Manual
                                                   MODE SELECT


                          Table 719
              MODE SELECT Parameter List Header


       The medium type field must be set to zero.

       The block descriptor length field specifies the length,
       in bytes,  of the block descriptor.  The drive supports
       zero or  one block descriptors, so the only valid block
       descriptor lengths are 0 and 8 bytes.


B    PARAMETER LIST BLOCK DESCRIPTOR FORMAT

       The MODE  SELECT block  descriptor immediately  follows
       the parameter  list header.   The drive does not report
       an  error  if  the  block  descriptor  is  not  in  the
       parameter list  (block descriptor  length equals zero).
       The block  descriptor is  defined in  Table 720,  MODE
       SELECT Parameter List Block Descriptor Format.




                          Table 720
      MODE SELECT Parameter List Block Descriptor Format


       The number of blocks field is ignored by the drive.

       The block  length field  specifies the  length  of  the
       logical block,  in bytes.   The  block length  must  be
       equal to,  or an exact multiple of, the physical sector
       size.   The disk  drive supports logical block sizes of
       256 to 4,096 bytes.

       Due to  the constraints  of the REASSIGN BLOCK command,
       it is  recommended that  the logical  block size be the
       same as  the physical  sector size.   When  the logical
       block  size  exceeds  the  physical  sector  size,  the
       REASSIGN BLOCK  command must  reassign all the physical
       sectors contained  in the logical block.  If the number
       of sectors  per logical  block exceeds  the  number  of
       spare sectors  per zone,  the entire zone is reassigned
       whenever a REASSIGN BLOCK command is executed.

    XT-4000S Product Specification & OEM Technical Manual
MODE SELECT

C    PAGE HEADER FORMAT

       Each mode page contains a page code length and a set of
       mode parameters.   The  page codes are defined in Table
       721.   The page  code field  identifies the format and
       parameters defined for that mode page.




                          Table 721
                    MODE SELECT Page Codes


       The page  length field  specifies the length, in bytes,
       of the  mode parameters  that follow.  If the initiator
       does not  set this  value to the value that is returned
       for the  page by  the MODE  SENSE  command,  the  drive
       returns CHECK  CONDITION status.  The sense data is set
       to ILLEGAL REQUEST/INVALID FIELD IN PARAMETER LIST.


7.4.4     Error Recovery Parameters Page

       This section  specifies the  mode  parameters  for  the
       error recovery  options supported  by the  drive.   The
       format for  the error  recovery page  (page code  1) is
       shown in Table 722, Error Recovery Page (Page Code 1).
       A copy  of each  of these  parameters is saved for each
       initiator.  This allows any initiator to change its own
       parameters without  affecting  the  parameters  of  any
       other initiator.




                          Table 722
              Error Recovery Page (Page Code 1)


       NOTE: The drive  saves this page whenever the initiator
       issues a  FORMAT UNIT,  or MODE  SELECT command ,  with
       the save parameters (SP) bit set to one.

       An automatic  write reallocation  enabled (AWRE) bit of
       one indicates  that the  drive  will  enable  automatic
       reallocation of  defective data  blocks detected during
       write operations.   All error recovery actions required
       by the error recovery bits (EER, PER, DTE, and DCR) are
       executed.  The automatic reallocation is performed only
       if the  drive encounters  a BLOCK  NOT FOUND  (03h/14h)
       during the write process.  The defective sector is then

    XT-4000S Product Specification & OEM Technical Manual
                                                   MODE SELECT

       relocated and  the write  data is  then placed  in  the
       reallocated block.   Error reporting as required by the
       error recovery  bits is performed only after completion
       of the  reallocation.   The drive presents any failures
       that  occur  during  the  reallocation  process.    The
       automatic reallocation  process follows  the same error
       procedures as the REASSIGN BLOCKS command.

       An AWRE  bit of  zero indicates that the drive does not
       perform automatic reallocation of defective data blocks
       during write operations.

       An automatic  read reallocation  enabled (ARRE)  bit of
       one indicates  that the  drive  will  enable  automatic
       reallocation  of  defective  data  blocks  during  read
       operations.  All error recovery actions required by the
       error recovery  bits (TB,  EER, PER,  DTE, and DCR) are
       executed.  The automatic reallocation is then performed
       only if the target successfully recovers the data.  The
       recovered data is then placed in the reallocated block.
       Error reporting  as required by the error recovery bits
       is performed only after completion of the reallocation.
       The drive  presents any  failures that occur during the
       reallocation  process.     The  automatic  reallocation
       process  follows  the  same  error  procedures  as  the
       REASSIGN BLOCKS command.

       An ARRE bit of zero indicates that the target shall not
       perform automatic reallocation of defective data blocks
       during read  operations.   See Figure  71 for  a  flow
       chart of automatic read reallocation.




                          Figure 71
             Flow Chart of Automatic Reallocation


       A transfer  block (TB)  bit of  one specifies  that the
       drive transfers  the block  with the  data error before
       terminating the  command.   This bit is only applicable
       when an  unrecoverable data  error is  encountered,  or
       when the  disable transfer on error (DTE) bit is set to
       one and  a recoverable  error is  encountered.  If this
       bit is zero, the drive does not transfer the block with
       the data  error.   In both cases, the drive reports the
       address of  the block  with the error, rather than that
       of the  preceding block,  in the  sense data.   If  the
       transfer terminates with other than a data error (i.e.,
       data not found), the drive does not transfer the block.

    XT-4000S Product Specification & OEM Technical Manual
MODE SELECT

       A read  continuous (RC) bit of one overrides the enable
       early  correction  (EEC),  disable  transfer  on  error
       (DTE), post  error (PER),  and disable correction (DCR)
       bits, and  disables all  retries and  data  correction.
       The transfer  block (TB)  bit is  not applicable.  When
       the read  continuous (RC)  bit is set to one, the drive
       transfers the  entire requested  length of data without
       adding delays  that are  caused by  its error  recovery
       schemes.   The drive sends data which may be erroneous,
       or fabricated,  to maintain  a continuous  flow of data
       and avoid delays.

       An enable  early correction  (EEC) bit of one specifies
       that the  drive does not exhaust the retry count before
       attempting any  ECC correction.  When this bit is zero,
       the drive  exhausts the  retry count before it attempts
       any ECC  correction.    Also,  the  drive  attempts  to
       recover the  data, using  head offset  and data  strobe
       offset, before attempting ECC correction.

       NOTE: This field  does not  disable retries during seek
       operations.   For any  seek or  positioning error,  the
       drive performs  a recalibrate  operation, then  retries
       the seek  operation.  If the second attempt also fails,
       the drive terminates the command.

       A post  error (PER)  bit of  one instructs the drive to
       report any  recoverable errors  to the initiator.  This
       error is  either reported immediately, or at the normal
       completion of  the command,  depending on  the state of
       the disable transfer on error (DTE) bit.  The drive may
       terminate the  data transfer  before all  data has been
       transferred, depending on the error encountered and the
       states of  the other  error recovery  bits in byte two.
       When set  to zero, this bit suppresses the reporting of
       recovered  errors.     Unrecovered  errors  are  always
       reported.

       A disable transfer on error (DTE) bit of one and a post
       error (PER)  bit of one instruct the drive to terminate
       the command  immediately when  a recoverable  error  is
       encountered, and  create the  CHECK  CONDITION  status.
       The drive may or may not transfer the data contained in
       the block  in error,  depending on  the setting  of the
       transfer block  (TB) bit.   The  initiator can only set
       the disable  transfer on  error (DTE)  bit to one if it
       has set  the post  error (PER)  bit to  one.    If  the
       disable transfer  on error  (DTE) bit is zero, the disk
       drive continues  the data  transfer when  a recoverable
       error is  encountered.   When disable transfer on error
       (DTE) equals zero, and post error (PER) equals one, the

    XT-4000S Product Specification & OEM Technical Manual
                                                   MODE SELECT

       sense data  reports the  last  recoverable  error  that
       occurred within a transfer.

       A disable  correction (DCR)  bit of  one  disables  ECC
       correction when  reading a  sector from  the drive.  No
       correction is attempted, and if a correctable ECC error
       occurs it is treated as an unrecoverable error.

       The retry  count field  specifies the maximum number of
       retries to  attempt when  an error is encountered.  The
       drive supports retry counts from 0 to 255.  The default
       is 16.

       The correction  span field  specifies the  largest read
       data  error,  in  bits,  on  which  correction  may  be
       attempted.   The drive  supports a correction span of 0
       to 17 bits.  The default is 12.

       The  head   offset  count   field  specifies  a  forced
       incremental offset,  from the  center of  the track, to
       use when performing a disk read operation.  When set to
       zero, the  disk drive  does not apply any offset.  When
       set to  a positive  value, the drive applies the offset
       in an  increasing distance in the direction of the next
       physical track.   When  set to  a twos  complement, the
       drive applies  the offset  in an increasing distance in
       the opposite  direction of a positive value.  The drive
       supports three  levels of  offset  in  each  direction.
       This field  has no  effect on  offsets  used  in  retry
       procedures.

       The data  strobe offset count field is not supported by
       the drive and must be set to zero.

       The recovery  time limit  field is not supported by the
       drive and must be set to FFh.

       Table 723, MODE SELECT Error Recovery Modes, lists the
       possible error recovery modes which may occur using the
       above parameters.   Those  combinations  which  do  not
       provide any  useful function, i.e., terminate on errors
       but do  not report them, are marked as invalid mode and
       should  not   be  selected  by  the  initiator.    Data
       transfers terminate  immediately for  any unrecoverable
       error.



                          Table 723
               MODE SELECT Error Recovery Modes

    XT-4000S Product Specification & OEM Technical Manual
MODE SELECT

7.4.5     Disconnect-Reconnect Page

       This section  describes the  disconnect-reconnect  mode
       parameters  supported   by  the   drive.    These  mode
       parameters  modify  the  disconnect-reconnect  strategy
       used by  the drive.   Refer  to  Appendix  B  for  more
       information.   The format  for the disconnect-reconnect
       page is shown in Table 724, Disconnect-Reconnect Page.
       The drive  saves a  copy of  these parameters  for each
       initiator.  This allows any initiator to change its own
       parameters without  affecting the  parameters of  other
       initiators.




                          Table 724
                  Disconnect-Reconnect Page


       NOTE: The drive  saves this page whenever the initiator
       issues a  MODE SELECT command, with the save parameters
       (SP) bit set to one.

       The buffer  full ratio indicates to the target, on read
       operations, how  full the  buffer should  be  prior  to
       attempting a  reselection.    The  buffer  empty  ratio
       indicates to the target, on write operations, how empty
       the buffer should be prior to attempting a reselection.

       The performance  benefit from using buffer ratios is in
       a multi-target  environment where  SCSI bus utilization
       is critical.   Proper  use of  the  buffer  ratios  can
       ensure  maximum   utilization  of   the  SCSI  bus,  by
       minimizing the time to transfer data.

       The buffer  ratio is  the percentage  of the buffer, or
       the  transfer  length,  whichever  is  less.    If  the
       transfer length  is less  than the  buffer, the  buffer
       ratio will  be applied  to the transfer length.  If the
       transfer length  is greater than the buffer, the buffer
       ratio will  be applied  to the buffer size.  The buffer
       full and  buffer  empty  ratios  are  numerators  of  a
       fractional multiplier  that has 256 as its denominator.
       A value  of zero  indicates that  the target  initiates
       reselection as  soon as one sector of data is available
       (default).   A value  of 255 indicates that 100% of the
       data transfer is in the buffer or the buffer was filled
       with data  before reselection, whichever is applicable.
       See appendix B for further information.

    XT-4000S Product Specification & OEM Technical Manual
                                                   MODE SELECT

       The bus  inactivity limit  field specifies  the maximum
       time, in  100 microsecond  increments, that  the  drive
       will stay  connected to  the SCSI  bus without  any bus
       activity.   The  drive  supports  a  range  of  1  (100
       microseconds) to 650 (65,000 microseconds).  A value of
       zero in  this field  means the drive can stay connected
       to the bus indefinitely.  The default is 10

       The disconnect time limit field is not supported by the
       drive and must be set to zero.

       The connect  time limit  field is  not supported by the
       drive and must be set to zero.


7.4.6     Format Device Page

       This  section   specifies  the   format   device   mode
       parameters supported  by the drive.  The format for the
       format device  page is  shown  in  Table  725,  Format
       Device Page

       NOTE: The drive  saves this page whenever the initiator
       issues a FORMAT UNIT command.




                          Table 725
                      Format Device Page


       The tracks  per zone  field  specifies  the  number  of
       tracks per  zone to use in dividing the capacity of the
       drive for  the purpose of allocating alternate sectors.
       The drive  supports either  one track,  or one cylinder
       per zone.   This  field may be set to either one or the
       number of data heads in the drive.

       The alternate  sectors per  zone  field  specifies  the
       number of alternate sectors per zone to allocate during
       formatting.   If the  tracks per zone field equals one,
       the drive  supports up  to three alternate sectors.  If
       the tracks  per zone  field equals  the number  of data
       heads, the  drive supports  up to  one  less  than  the
       number of  sectors per  track alternate  sectors.   The
       default is 5 alternate sectors per zone.

       The alternate  tracks per zone field is not used by the
       drive and must be set to zero.

    XT-4000S Product Specification & OEM Technical Manual
MODE SELECT

       The alternate  tracks per  volume field  specifies  the
       number of  tracks per  drive to  deallocate, for defect
       handling during  a format operation.  A track is mapped
       onto  the  alternate  tracks  by  the  FORMAT  UNIT  or
       REASSIGN BLOCK  commands, when  relocation occurs  in a
       zone whose alternate sectors have been exhausted.

       NOTE: The  drive   rounds  the   number  of  tracks  to
       deallocate up  to the  nearest cylinder  boundary.  The
       drive supports  from 0  to  255  alternate  tracks  per
       volume, in  multiples of  tracks  per  cylinder.    The
       default is  3  cylinders  allocated  (For  example,  45
       tracks on  an XT-8760, 24 on an XT-8380S, and 21 on XT-
       4170S and XT-4380S.)

       The sectors  per track  field specifies  the number  of
       physical sectors  per track.   If  this field is set to
       zero, the  drive calculates the sectors per track based
       on the  value in  the data  bytes per  physical  sector
       field.

       The data  bytes per physical sector field specifies the
       number  of  bytes  per  physical  sector.    The  drive
       supports sector  sizes from  256  to  4,096  bytes  per
       sector.

       The interleave field is ignored by the drive and may be
       set to  any value.   The interleave value is set in the
       FORMAT UNIT command.

       The track  skew field  specifies the number of physical
       sectors between the last logical block of one track and
       the first logical block on the next sequential track on
       the same  cylinder.   It is recommended that this value
       always be set to zero, since the drive does not require
       head switching  time.  The track skew cannot exceed the
       value in the sectors per track field.

       The  cylinder   skew  field  specifies  the  number  of
       physical sectors  between the last logical block of one
       cylinder and  the  first  logical  block  of  the  next
       sequential cylinder.   By  setting this field to FFFFh,
       the initiator  requests  that  the  drive  compute  the
       optimum value, based on the selected sector size.

       The soft  sector format (SSEC) bit cannot be set by the
       MODE SELECT  command and  the drive  ignores this field
       (see 7.5 MODE SENSE later in this chapter).

       The hard  sector format (HSEC) bit cannot be set by the
       MODE SELECT  command and  the drive  ignores this field
       (see 7.5 MODE SENSE later in this chapter).

    XT-4000S Product Specification & OEM Technical Manual
                                                   MODE SELECT

       The removable  media (RMB) bit is not used by the drive
       and must be set to zero.

       The surface  (SURF) bit  is not  supported by the drive
       and must be set to zero.


7.4.7     Rigid Disk Drive Geometry Parameters Page

       This section defines the rigid disk drive geometry mode
       parameters supported  by the drive.  The format for the
       rigid disk  drive geometry page is shown in Table 726,
       MODE SELECT  Rigid Disk Drive Geometry Parameters (Page
       Code 4).

       NOTE: The drive  saves this page whenever the initiator
       issues a FORMAT UNIT command.




                          Table 726
MODE SELECT Rigid Disk Drive Geometry Parameters (Page Code 4)


       The maximum  number of  cylinders field  specifies  the
       maximum number  of cylinders  available on  the medium.
       This value, minus the alternate tracks per volume value
       (converted to cylinders), and minus the three cylinders
       reserved by  the  disk  drive,  equals  the  number  of
       cylinders  addressable   by  the   user.     The   most
       significant byte (MSB), byte two, must be set to zero.

       The maximum  number of heads field specifies the number
       of data  heads on the drive.  The drive supports one to
       fifteen heads.

       The starting  cylinder - write precompensation field is
       not supported by the drive and must be set to zero.

       The starting  cylinder - reduced write current field is
       not supported by the drive and must be set to zero.

       The drive step rate field is not supported by the drive
       and must be set to zero.

       The landing zone cylinder field is not supported by the
       drive and must be set to zero.

    XT-4000S Product Specification & OEM Technical Manual
MODE SELECT

7.4.8     Caching Page

       The caching parameters page defines the parameters that
       affect the  use of  the read-ahead  cache.   See  Table
       727, Caching Page.




                          Table 727
                         Caching Page


       The write  cache enable  (WCE) bit  is not supported by
       the drive and must be set to zero.

       The multiplication  factor (MF) bit is not supported by
       the drive and must be set to zero.

       A read  cache disable  (RCD) bit of zero specifies that
       the target  may return data requested by a READ command
       by accessing  either the  cache or media.  A RCD bit of
       one specifies that the target shall transfer all of the
       data requested by a READ command from the medium (i.e.,
       data cannot be transferred from the cache).

       The  demand   read  retention  priority  field  is  not
       supported by the drive and must be set to zero.

       The write  retention priority field is not supported by
       the drive and must be set to zero.

       The disable  pre-fetch transfer  length  field  is  not
       supported by the drive and must be set to zero.

       The minimum  pre-fetch field  is not  supported by  the
       drive and  must be  set to  zero.   Setting the minimum
       pre-fetch field  to zero,  causes the  read-ahead to be
       terminated  whenever   another  command  is  ready  for
       executing.

       The maximum  pre-fetch field  is not  supported by  the
       drive and must be set to zero.

       The maximum pre-fetch ceiling field is not supported by
       the drive and must be set to zero.


7.4.9     Maxtor Drive Control Page

       Maxtor drive  control parameters  are in page code 32h.
       This vendor  unique page allows greater flexibility for

    XT-4000S Product Specification & OEM Technical Manual
                                                   MODE SELECT

       custom firmware  requirements.   See Table 728 for the
       format of the Maxtor Drive Control Page.




                          Table 728
                  Maxtor Drive Control Page


       Bytes two  and three  specify unique  firmware and user
       options.

       An enable synchronous data transfer request (ESDTR) bit
       of zero  specifies that  the target  comply with SCSI-2
       for negotiating  a synchronous data transfer.  An ESDTR
       bit of  one specifies  that  following  a  power-on  or
       reset,  the   target  will   not  initiate   the  first
       negotiations for  a synchronous  data  transfer.    The
       default condition is one.

       A  format  data  pattern  enable  (FDPE)  bit  of  zero
       specifies that when byte 2 (format data pattern) in the
       FORMAT UNIT  command contains  00h, the default pattern
       of E5h  be used  for the  format data pattern.  An FDPE
       bit of  one specifies  that  the  target  not  use  the
       default pattern.   The data pattern of 00h will be used
       in place of the default pattern.  The default condition
       is zero.

       A contingent  reservation (CR)  bit of  zero  specifies
       that the  target comply  with SCSI-2  and not  set up a
       contingent reservation.  A CR bit of one specifies that
       an "implied reservation" condition be in effect for the
       active initiator  whenever a check condition occurs.  A
       check  condition   will  cause   the  target   to  send
       RESERVATION CONFLICT  status  to  any  other  initiator
       until the  check condition  is addressed  and a RELEASE
       UNIT command  is issued  by the  active initiator  or a
       SCSI bus reset occurs.  The default condition is zero.

       A disable  unit attention  (DUA) bit  of zero specifies
       that the  target comply  with  SCSI-2  after  reset  or
       power-up.   A DUA  bit of  one specifies that the drive
       will not  issue a  CHECK CONDITION for a UNIT ATTENTION
       condition after  reset or  on power-up.    The  default
       condition is zero.  *

       A START  bit of zero specifies that the target start up
       according to jumpers JP14 and JP38.  A START bit of one
       allows the  drive to  start as soon as power is applied

    XT-4000S Product Specification & OEM Technical Manual
MODE SELECT

       regardless of  the jumper  configurations.   Subsequent
       START commands  will be  accepted without  error.   The
       default condition is zero.  *

       A software  selectable ID  (SSID) bit of zero specifies
       that the  drive SCSI ID will be determined by the value
       set by  jumpers JP35,  JP36, and JP37 on the drive PCB.
       An SSID  bit of  one specifies  that the  drive SCSI ID
       will be  determined by  the value  of the  SCSI address
       (SCSIADR) bits and the value set by the jumpers will be
       ignored.  The default condition is zero.  *

       The SCSI  address (SCSIADR)  bits determine the SCSI ID
       if the  SSID bit  is set to one.  The default condition
       is 000b.  *

       Bytes  four  through  seven  are  reserved  for  future
       applications or parameters and are set to zero.

       * These bits are supported in products that incorporate
       EEPROM.


7.4.10    Read-Ahead Control Page

       This section  describes  the  read-ahead  control  mode
       parameters supported  by the drive.  The format for the
       read-ahead control  page is  shown in Table 729, Read-
       Ahead Control Page (Page Code 38h).




                          Table 729
           Read-Ahead Control Page (Page Code 38h)


       If the  read-ahead with  mechanical delay (RAMD) bit is
       set to  one, read-ahead  will not  stop when  a SEEK is
       required.  This includes a SEEK to the next cylinder or
       a SEEK  to an  alternate track.   An  RAMD bit  of zero
       stops Read-Ahead whenever a SEEK is required.

       A cache  enable (CE)  bit of one enables read-ahead.  A
       CE bit of zero disables read-ahead.

       The cache table size field is non-changeable and set to
       0001b.

       The prefetch  threshold field is non-changeable and set
       to FFh.   An  FFh value  indicates that  Read-Ahead (if

    XT-4000S Product Specification & OEM Technical Manual
                                                   MODE SELECT

       enabled by  the CE  bit)  is  performed  for  all  READ
       commands, regardless  of  the  transfer  length.    The
       prefetch threshold  field is  the maximum  value of the
       transfer length  (as specified  in the CDB) for which a
       Read-Ahead operation is performed.
       The maximum  prefetch field  is non-changeable  and  is
       reported as  the  number  of  logical  blocks  (at  the
       current block  length) which can be stored in the Read-
       Ahead buffer,  which is  45,056  bytes.    The  maximum
       prefetch field  is the  maximum number  of data  blocks
       which are prefetched by a Read-Ahead operation.


7.4.11    Error Conditions

       If any  field not used or supported by the drive is not
       set to  zero, the drive returns CHECK CONDITION status.
       The sense  data is set to ILLEGAL REQUEST/INVALID FIELD
       IN PARAMETER LIST (05h/26h).

       If the  medium type  is not  set  to  zero,  the  drive
       returns CHECK  CONDITION status.  The sense data is set
       to ILLEGAL  REQUEST/INVALID  FIELD  IN  PARAMETER  LIST
       (05h/26h).

       If a  block descriptor  length of  other than  zero  or
       eight is  specified, the  drive returns CHECK CONDITION
       status.     The  sense   data  is   set  to     ILLEGAL
       REQUEST/INVALID FIELD IN PARAMETER LIST (05h/26h).

       If the  density code  is not  set to  zero,  the  drive
       returns CHECK  CONDITION status.  The sense data is set
       to   ILLEGAL REQUEST/INVALID  FIELD IN  PARAMETER  LIST
       (05h/26h).

       If the  bytes per  physical sector is less than 256, or
       greater than  4,096, the  drive returns CHECK CONDITION
       status.     The  sense   data   is   set   to   ILLEGAL
       REQUEST/INVALID FIELD IN PARAMETER LIST (05h/26h).

       If the  track skew  parameter  exceeds  the  number  of
       sectors per  track, the  drive returns  CHECK CONDITION
       status.     The  sense   data  is   set  to     ILLEGAL
       REQUEST/INVALID FIELD IN PARAMETER LIST(05h/26h).

       If the  cylinder skew  parameter exceeds  the number of
       sectors  per  track  (except  for  0FFFFh),  the  drive
       returns CHECK  CONDITION status.  The sense data is set
       to ILLEGAL  REQUEST/INVALID  FIELD  IN  PARAMETER  LIST
       (05h/26h).

    XT-4000S Product Specification & OEM Technical Manual
MODE SELECT

       If the  tracks per  zone field is not set to zero, one,
       or  the  number  of  heads,  the  drive  returns  CHECK
       CONDITION status.   The  sense data  is set  to ILLEGAL
       REQUEST/INVALID FIELD IN PARAMETERS LIST (05h/26h).

       If the  saved MODE SELECT configuration information has
       been destroyed,  and the initiator issues a MODE SELECT
       command with  a save  parameters (SP)  bit of  one, the
       drive returns  CHECK CONDITION  status.  The sense data
       is set  to NOT  READY/ILLEGAL FUNCTION  FOR DEVICE TYPE
       (02h/22h) .

       If the  alternate sectors  per zone  field value is not
       within the  supported range,  the drive  returns  CHECK
       CONDITION status.   The  sense data  is set  to ILLEGAL
       REQUEST/INVALID FIELD IN PARAMTERS LIST (05h/26h).
       If the initiator specifies an invalid mode in the error
       recovery  bits,   the  drive  returns  CHECK  CONDITION
       status.       The   sense  data   is  set   to  ILLEGAL
       REQUEST/INVALID FIELD IN PARAMETER LIST (05h/26h).

       If, in  the rigid  drive geometry  parameters page, the
       drive receives  a value  in the maximum number of heads
       field that is greater than the actual maximum number of
       heads, the  drive returns  CHECK CONDITION status.  The
       sense data  is set  to ILLEGAL REQUEST/INVALID FIELD IN
       PARAMETER LIST (05h/26h).

       If the  page length  byte in  each page header does not
       match the  page length,  as specified  in this document
       and returned  by the  MODE  SENSE  command,  the  drive
       returns CHECK  CONDITION status.  The sense data is set
       to ILLEGAL  REQUEST/INVALID  FIELD  IN  PARAMETER  LIST
       (05h/26h).

    XT-4000S Product Specification & OEM Technical Manual
MODE SENSE
    XT-4000S Product Specification & OEM Technical Manual
                                                    MODE SENSE


7.5  MODE SENSE

       The MODE  SENSE command  provides a  means by which the
       initiator  may  receive  various  parameters  from  the
       drive.   MODE SENSE  is a  complementary command to the
       MODE SELECT command.

       The drive sends blocks of parameters that are separated
       into pages.   These  pages specify  various options and
       features which  the initiator may change.  Each page is
       preceded by  a page  code and  the length  of the page.
       The page  length value  does not  include bytes zero or
       one.

       The drive  maintains the  following four different sets
       of MODE SENSE data:

         Default Values:   The  default values  are  obtained
          from  the  drive's  programmable  read  only  memory
          (PROM), the media, and the drive jumpers.

         Saved Values:   The saved values are the MODE SELECT
          parameters saved  by the  drive on the medium.  This
          is done  when  the  drive  performs  a  FORMAT  UNIT
          command for  pages 3  and 4, or MODE SELECT command,
          with the  save parameters  (SP) bit  set to one, for
          pages 1, 2, 8, and 38.

         Current Values:   The  current values  are the  MODE
          SELECT parameters  used by  the drive  during normal
          operation.   Any MODE SELECT command issued, changes
          the current values.

         Changeable Values:   The changeable values are those
          parameters  supported  by  the  drive  that  can  be
          changed by the MODE SELECT command.

       At initialization  time, a  POWER ON or RESET condition
       has occurred, see Chapter 4.0, User Selectable Options.
       After the  drive spins  up, it  reads the  saved values
       from the drive and copies them into the current values.

       When the  drive completes  a FORMAT  UNIT  command,  it
       writes all  supported pages  to the  medium.    (On  an
       unformatted drive,  the current parameters are the same
       as the  default parameters.)   The  initiator may  then
       change   the   current   parameters   upon   successful
       completion  of   the  MODE   SELECT  command  prior  to
       formatting the  drive.   When the  FORMAT UNIT  command
       completes, the  drive writes  the  current  values  for

    XT-4000S Product Specification & OEM Technical Manual
MODE SENSE

       pages 3  and 4  (which may  have been changed by a MODE
       SELECT command) to the medium as the saved values.


7.5.1     SCSI Deviations

       MODE SENSE  data for  pages 1  and 2  (both current and
       saved values) are maintained separately for each of the
       seven possible  initiators.   This avoids the necessity
       of  reporting   a  UNIT   ATTENTION  condition  to  all
       initiators when  one initiator  has  changed  the  mode
       parameters.


7.5.2     Command Parameters

       The MODE  SENSE command description block is defined in
       Table 730, MODE SENSE Command.




                          Table 730
                      MODE SENSE Command


       The page control field (PCF) indicates the type of page
       values  the   drive  returns:     current,  changeable,
       default, or saved.  Table 731, MODE SENSE Page Control
       Fields, lists and describes the page control fields.




                          Table 731
                MODE SENSE Page Control Fields


       A  page code field indicates the page(s) to be returned
       in the  MODE SENSE  data.   Table 732, MODE SENSE Page
       Codes, lists and describes the page codes.  If a single
       page is requested, the drive only returns the requested
       page.   The block descriptor information is always sent
       with MODE SENSE data.




                          Table 732
                    MODE SENSE Page Codes

    XT-4000S Product Specification & OEM Technical Manual
                                                    MODE SENSE

       The allocation  length field  indicates the  number  of
       bytes the  initiator has  allocated for  returned  MODE
       SENSE data.  If the drive receives a zero value in byte
       four, it  does not transfer any data and does not treat
       this condition  as an  error.    A  nonzero  allocation
       length value  indicates the  maximum number of bytes to
       be transferred.  The drive terminates the DATA IN phase
       when the  number of  bytes which  have been transferred
       reaches the  value of  the allocation  length field, or
       when all available MODE SENSE data has been transferred
       to the initiator, whichever is less.


7.5.3     Parameter List Format

       The MODE  SENSE data  is  sent  by  the  drive  to  the
       initiator during the DATA IN phase.  This data consists
       of a  parameter list  header, one block descriptor, and
       the specified page descriptors.

       The  parameter   list  header  is  4  bytes  long,  and
       specifies the  medium type  and the length of the block
       descriptor.

       The block descriptor is 8 bytes long, and specifies the
       density code,  the number  of  blocks,  and  the  block
       length.

       The  page   descriptors  contain   various   parameters
       separated into pages.  These parameters specify various
       options and  features which  the initiator  may  change
       with the  MODE SELECT  command.   The type of page data
       returned is  specified with  the  page  code  and  page
       control field (PCF) in the CDB.

       Each defined  page is  preceded by  a header of 2 bytes
       that specifies  the page code and the page length.  The
       page code  identifies the  meaning of  the bytes  which
       follow it.   The page length field indicates the number
       of bytes  supported by  the disk  drive for  that page.
       The page length value does not include the page code on
       page length  bytes.   After the  header, the  pages are
       separated  into  sub-blocks  that  contain  a  list  of
       related flags and/or values.


A    PARAMETER LIST HEADER FORMAT

       The MODE  SENSE parameter list header is the first part
       of the  parameter list.   The  header is  formatted  as
       shown in Table 733, MODE SENSE Parameter List Header.

    XT-4000S Product Specification & OEM Technical Manual
MODE SENSE



                          Table 733
               MODE SENSE Parameter List Header


       The sense data length field indicates the length of the
       data that  is sense, returned when a MODE SENSE command
       is issued.   This  length does  not  include  the  data
       length field  itself.   The sense  data  length  varies
       depending on which page(s) are requested.

       The medium  type field  indicates the media type on the
       drive.  The drive always returns a medium type of zero.

       A write  protect (WP) bit of one indicates the drive is
       write protected.   When  the write  protect (WP) bit is
       set to zero, the drive is not write protected.

       The block  descriptor length field indicates the length
       of the block descriptor and is set to eight.


B    PARAMETER LIST BLOCK DESCRIPTOR FORMAT

       The  MODE   SENSE  parameter   list  block   descriptor
       immediately follows  the parameter  list header.    The
       block descriptor  is formatted  as shown in Table 734,
       MODE SENSE Parameter List Block Descriptor Format.




                          Table 734
      MODE SENSE Parameter List Block Descriptor Format


       The density code field defines the density of the media
       on the  addressed disk  drive.   The density code has a
       value of  zero, to indicate only the default density of
       the medium is supported.

       The number  of blocks  field indicates the total number
       of logical  blocks which  use media of the density code
       defined in  byte zero.   The  number  of  blocks  field
       always returns  zeros to  indicate that all blocks have
       the same media type.

       The logical  block length field indicates the length of
       the logical block, in bytes.

    XT-4000S Product Specification & OEM Technical Manual
                                                    MODE SENSE

C    PAGE HEADER FORMAT

       Each of  the optional page descriptors is preceded by a
       page header.   The  page header  is 2  bytes  long  and
       identifies the  page type  length.  Each page header is
       immediately  followed   by   its   corresponding   page
       parameters.

       The page  code field  identifies the  page type.  Table
       735, MODE SENSE Page Header Page Codes, lists the page
       codes and their corresponding page descriptions.




                          Table 735
              MODE SENSE Page Header Page Codes


       The page  length field indicates the number of bytes in
       the page, not including the page length byte.

7.5.4     Error Recovery Parameters Page

       This subsection  specifies  the  format  of  the  error
       recovery parameter  page (page  code 1), as returned by
       the MODE  SENSE command  (see Table  736,  MODE  SENSE
       Error Recovery  Parameters (Page  Code 1)).   A copy of
       each of  these parameters  is saved for each initiator.
       The values  returned are  for the  initiator which sent
       the MODE SENSE command.




                          Table 736
      MODE SENSE Error Recovery Parameters (Page Code 1)


       A parameter  savable (PS) bit of one indicates the that
       drive saves  the parameters  supported  in  this  page.
       When the  parameter savable (PS) bit is zero, the drive
       does not  save the  page parameters.   The drive always
       returns a one in this field.

       An automatic  write reallocation  enabled (AWRE) bit of
       one indicates  that the  drive  will  enable  automatic
       reallocation of  defective  data  blocks  during  write
       operation.   All error recovery actions required by the
       error recovery  bits  (EER,  PER,  DTE,  and  DCR)  are
       executed.  The automatic reallocation is performed only

    XT-4000S Product Specification & OEM Technical Manual
MODE SENSE

       if the  drive encounters  a BLOCK  NOT FOUND  (03h/14h)
       during the write process.  The defective sector is then
       relocated and  the write  data is  then placed  in  the
       reallocated block.   Error  posting as  required by the
       error recovery  bits is performed only after completion
       of the  reallocation.   The drive presents any failures
       that  occur  during  the  reallocation  process.    The
       automatic reallocation  process follows  the same error
       procedures as the REASSIGN BLOCKS command.

       An AWRE  bit of  zero indicates that the drive does not
       perform automatic reallocation of defective data blocks
       during write operations.

       An automatic  read reallocation  enabled (ARRE)  bit of
       one indicates  that the  drive  will  enable  automatic
       reallocation  of  defective  data  blocks  during  read
       operations.  All error recovery actions required by the
       error recovery  bits (TB,  EER, PER,  DTE, and DCR) are
       executed.  The automatic reallocation is then performed
       only if the target successfully recovers the data.  The
       recovered data is then placed in the reallocated block.
       Error posting as required by the error recovery bits is
       performed only  after completion  of the  reallocation.
       The drive  presents any  failures that occur during the
       reallocation  process.     The  automatic  reallocation
       process  follows  the  same  error  procedures  as  the
       REASSIGN BLOCKS command.

       An ARRE bit of zero indicated that the target shall not
       perform automatic reallocation of defective data blocks
       during read  operations.   See Figure  71 for  a  flow
       chart of automatic read reallocation.

       A   transfer block  (TB) bit  of one indicates that the
       drive should  transfer the  block with  the data  error
       before terminating  the command.    This  bit  is  only
       applicable when  unrecoverable error is encountered, or
       when the  disable transfer on error (DTE) bit is set to
       one, and  a recoverable  error is  encountered.  If the
       transfer block  (TB) bit  is zero,  the drive  does not
       transfer the block with the data error.  In both cases,
       the drive  reports the  block address of the block with
       the error,  rather than that of the preceding block, in
       the sense  data.  If the transfer terminates with other
       than a  data error (i.e., data not found), the block is
       not  transferred.    If  the  initiator  requested  the
       changeable values,  the transfer  block (TB) bit is set
       to one.

    XT-4000S Product Specification & OEM Technical Manual
                                                    MODE SENSE

       A read  continuous (RC) bit of one overrides the enable
       early  correction  (EEC),  disable  transfer  on  error
       (DTE), post  error (PER),  and disable correction (DCR)
       bits, and  disables all  retries and  data  correction.
       The transfer  block (TB)  bit is  not applicable.  When
       the read  continuous (RC)  bit is set to one, the drive
       transfers the  entire requested  length of data without
       adding delays  that are  caused by  its error  recovery
       schemes.   The drive sends data which may be erroneous,
       or fabricated,  to maintain  a continuous  flow of data
       and avoid  delays.   If  the  initiator  requested  the
       changeable values, this bit is set to one.

       The enable  early correction  (EEC) bit  indicates that
       the drive  should perform  a minimum  number of retries
       before applying  any correction  algorithm.   When this
       bit is  set to one, the disk drive does not exhaust the
       retry count before attempting any ECC correction.  When
       this bit  is set  to zero, the drive exhausts the retry
       count, before  it attempts  any ECC correction.  If the
       initiator requested  the changeable values, this bit is
       set to one.

       NOTE: The enable  early correction  (EEC) bit  does not
       disable retries  during seek  operations.  For any seek
       or positioning  error, the  drive issues  a RECALIBRATE
       command to  the  disk  drive,  then  retries  the  seek
       operation.  If the second attempt also fails, the drive
       terminates the command.

       A post  error (PER)  bit of  one instructs the drive to
       report any  recoverable errors  to the initiator.  This
       error is  either reported immediately, or at the normal
       completion of  the command,  depending on  the state of
       the disable  transfer on  error (DTE)  bit.   The error
       reported to the initiator is the last error encountered
       during the  data transfer.   If  multiple errors occur,
       the drive  reports (in the sense information) the block
       address of either 1) the last block where the recovered
       error  occurred;   or  2)  the  block  with  the  first
       unrecoverable error.   If  the initiator  requested the
       changeable values,  the post  error (PER) bit is set to
       one.

       A disable transfer on error (DTE) bit of one and a post
       error (PER)  bit of one instruct the drive to terminate
       the command  immediately when  a recoverable  error  is
       encountered, and  create the  CHECK  CONDITION  status.
       The drive may or may not transfer the data contained in
       the block  in error,  depending on  the setting  of the
       transfer block  (TB) bit.   The  initiator can only set
       the disable  transfer on  error (DTE)  bit to one if it

    XT-4000S Product Specification & OEM Technical Manual
MODE SENSE

       has set  the post  error (PER)  bit to  one.    If  the
       disable transfer on error (DTE) bit is set to zero, the
       drive continues  the data  transfer when  a recoverable
       error is  encountered.   If the initiator requested the
       changeable values,  the disable transfer on error (DTE)
       bit is set to one.

       A disable  correction (DCR)  bit of  one  disables  ECC
       correction when  reading a  sector from  the drive.  No
       correction is attempted, and if a correctable ECC error
       occurs, it  is treated  as a recoverable error.  If the
       initiator requested  the changeable values, this bit is
       set to one.

       The retry  count field  indicates the maximum number of
       retries to  attempt when  an error is encountered.  The
       drive supports  retry counts  from 0  to 255 (decimal).
       If the  initiator requested the changeable values, this
       field is set to FFh.

       The correction  span field  indicates the  largest read
       data  error,  in  bits,  on  which  correction  may  be
       attempted.   The drive  supports a correction span of 0
       to 17  (decimal).    If  the  initiator  requested  the
       changeable values, this field is set to FFh.

       The  head   offset  count   field  indicates  a  forced
       incremental offset,  from the  center of  the track, to
       use when  performing  a  disk  operation.    The  drive
       supports three  levels of  offset  in  each  direction.
       This field  has no  effect on  offsets  used  in  retry
       procedures.

       The data  strobe offset count field is not supported by
       the drive and must be set to zero.

       The recovery time limit field  is not supported and the
       drive always returns FFh in this field.


7.5.5     Disconnect/Reconnect Parameters Page

       This   section    specifies   the    format   of    the
       disconnect/reconnect parameter  page (page  code 2), as
       returned by  the MODE  SENSE command  (see Table  737,
       MODE  SENSE   Disconnect/Reconnect  Control  Parameters
       (Page Code  2)).   The drive  saves a  copy of  each of
       these parameters  for each  initiator.  This allows any
       one initiator  to examine  its own  parameters  without
       affecting the parameters of any other initiator.

    XT-4000S Product Specification & OEM Technical Manual
                                                    MODE SENSE


                          Table 737
MODE SENSE Disconnect/Reconnect Control Parameters (Page Code
                              2)


       A parameter  savable (PS) bit of one indicates that the
       drive saves  the parameters  supported  in  this  page.
       When the  parameter savable (PS) bit is zero, the drive
       does not  save the  page parameters.   The drive always
       returns a one in this bit.

       The buffer  full ratio  field specifies  how  full  the
       internal buffer  will be before the drive reconnects to
       transfer the data to the initiator.

       The buffer  empty ratio  field indicates  how empty the
       internal buffer  will be before the drive reconnects to
       transfer more  data from the initiator.  See Appendix E
       for further information.

       The bus  inactivity limit field indicates the length of
       time, in  100 microsecond increments, that the drive is
       allowed to  stay connected  to the SCSI bus without any
       bus activity.   The  drive supports a range of 1 to 650
       (100  to   65,000  microseconds).    If  the  initiator
       requested the  changeable values,  this field is set to
       FFFFh.

       The disconnect  time limit  field is  not supported and
       the drive always returns a zero in this field.

       The connect  time limit  field is not supported and the
       drive always returns a zero in this field.


7.5.6     Direct-Access Device Format Parameters Page

       This section  specifies the format of the direct-access
       device  format   parameters  page  (page  code  3),  as
       returned by  the MODE  SENSE command  (see Table  738,
       MODE SENSE Direct-Access Device Format Parameters (Page
       Code 3)).




                          Table 738
 MODE SENSE Direct-Access Device Format Parameters (Page Code
                              3)

    XT-4000S Product Specification & OEM Technical Manual
MODE SENSE

       The  parameter  savable  (PS)  bit  is  always  one  to
       indicate that  the drive saves the parameters supported
       in this page.

       The tracks  per zone  field  indicates  the  number  of
       tracks per  zone.   The drive supports either one track
       per zone,  or n  tracks per zone, where n is the number
       of heads.   If  the initiator  requests the  changeable
       values, this field is set to FFFFh.

       The alternate  sectors per  zone  field  indicates  the
       number of alternate sectors per zone to allocate during
       formatting.  The disk drive supports from zero to three
       alternate sectors  per track,  or one  to n sectors per
       cylinder, where  n is  the number of sectors per track,
       minus one.   If  the initiator  requests the changeable
       values, this field is set to FFFFh.

       The alternate  tracks per  zone field is not supported,
       and the drive always returns a zero in this field.

       The alternate  tracks per  volume field  indicates  the
       number of  alternate tracks  to allocate, or the entire
       disk, during  formatting.   Bad tracks  are mapped onto
       the alternate  tracks by  the FORMAT  UNIT or  REASSIGN
       BLOCK  commands.     If   the  initiator  requests  the
       changeable values, this field is set to FFFFh.

       NOTE: The number  of alternate  tracks is rounded up to
       the nearest  cylinder boundary.   The  actual number of
       tracks is dependent on the number of heads.

       The sectors  per track  field indicates  the number  of
       physical sectors  per track.  If the initiator requests
       the changeable values, this field is set to FFFFh.

       The bytes  per  physical  sector  field  indicates  the
       number  of  bytes  per  physical  sector.    The  drive
       supports sectors  sizes of  256 to 4,096 bytes.  If the
       initiator requests the changeable values, this field is
       set to FFFFh.

       The interleave value field returns the interleave value
       specified in the FORMAT UNIT command when the drive was
       formatted.   If the  initiator requests  the changeable
       values, this field is set to 0000h.

       The track  skew field  indicates the number of physical
       sectors between the last logical block of one track and
       the first logical block of the next sequential track of
       the same  cylinder.   If  the  initiator  requests  the
       changeable values, this field is set to FFFFh.

    XT-4000S Product Specification & OEM Technical Manual
                                                    MODE SENSE

       The  cylinder   skew  field  indicates  the  number  of
       physical sectors  between the last logical block of one
       cylinder and  the  first  logical  block  of  the  next
       sequential cylinder.   The  default value  FFFFh  is  a
       dummy value,  which should  be used  in the MODE SELECT
       command to  indicate that  the drive  is to compute the
       value which  provides the  optimum  performance,  based
       upon the  selected bytes per physical sector field.  If
       the initiator  requests either  the  current  or  saved
       values, the  actual value  used is  reported.   If  the
       initiator requests the changeable values, this field is
       set to FFFFh.

       The soft  sector format (SSEC) bit is not supported and
       is always set to zero.

       The hard  sector format  (HSEC) bit  is set  to one  to
       indicate that  the drive  uses hard  sector formatting.
       If the  initiator requested the changeable values, this
       bit is set to zero.

       The removable  media (RMB)  bit is not supported and is
       always set to zero.

       The surface  (SURF) bit is not supported, and the drive
       always returns a zero in this bit.


7.5.7     Rigid Disk Drive Geometry Parameters Page

       This section defines the format of the rigid disk drive
       geometry page  (page code  4), as  returned by the MODE
       SENSE command  (see Table  739, MODE  SENSE Rigid Disk
       Drive Geometry Parameters (Page Code 4)).




                          Table 739
MODE SENSE Rigid Disk Drive Geometry Parameters (Page Code 4)


       A parameter  savable (PS) bit of one indicates that the
       drive saves  the parameters  supported  in  this  page.
       When the  parameter savable (PS) bit is zero, the drive
       does not  save the  page parameters.   The drive always
       returns a one in this bit.

       The maximum  number of  cylinders field  indicates  the
       maximum number  of cylinders  available on  the  drive.
       This value,  minus  the  alternate  tracks  per  volume
       (converted  to  cylinders),  and  the  three  cylinders

    XT-4000S Product Specification & OEM Technical Manual
MODE SENSE

       reserved by  the drive,  equals the number of cylinders
       addressable by the user.  If the initiator requests the
       changeable values, this field is set to FFFFFFh.

       The maximum  number of heads field indicates the number
       of data heads on the drive.  The default value for this
       field depends on the model number (see Table 740, MODE
       SENSE Default  Number of  Heads).    If  the  initiator
       requests the  changeable values,  this field  is set to
       FFh.




                          Table 740
              MODE SENSE Default Number of Heads


       The starting  cylinder - write precompensation field is
       not supported,  and the  drive always returns a zero in
       this field.

       The starting  cylinder - reduced write current field is
       not supported,  and the  drive always returns a zero in
       this field.

       The drive  step rate  field is  not supported,  and the
       drive always returns a zero in this field.

       The landing  zone cylinder  field is not supported, and
       the drive always returns a zero in this field.

7.5.8     Caching Page

       The caching parameters page defines the parameters that
       affect the  use of  the read-ahead  cache.   See  Table
       741, Caching Page.




                          Table 741
                         Caching Page


       The parameters  savable (PS)  bit is only used with the
       MODE SENSE command.  This bit is reserved with the MODE
       SELECT command.   A  PS bit  of one  indicates that the
       drive is capable of saving the page.

    XT-4000S Product Specification & OEM Technical Manual
                                                    MODE SENSE

       The write  cache enable  (WCE) bit  is not supported by
       the drive and must be set to zero.

       The multiplication  factor (MF) bit is not supported by
       the drive and must be set to zero.

       A read  cache disable  (RCD) bit of zero specifies that
       the target  may return data requested by a READ command
       by accessing  either the  cache or media.  A RCD bit of
       one specifies that the target shall transfer all of the
       data requested by a READ command from the medium (i.e.,
       data cannot be transferred from the cache).

       The  demand   read  retention  priority  field  is  not
       supported by the drive and must be set to zero.

       The write  retention priority field is not supported by
       the drive and must be set to zero.

       The disable  pre-fetch transfer  length  field  is  not
       supported by the drive and must be set to zero.

       The minimum  pre-fetch field  is not  supported by  the
       drive and  must be  set to  zero.   Setting the minimum
       pre-fetch field  to zero,  causes the  read-ahead to be
       terminated  whenever   another  command  is  ready  for
       executing.

       The maximum  pre-fetch field  is not  supported by  the
       drive and must be set to zero.

       The maximum pre-fetch ceiling field is not supported by
       the drive and must be set to zero.


7.5.9     Maxtor Drive Control Page

       Maxtor drive  control parameters  are in page code 32h.
       This vendor  unique page allows greater flexibility for
       custom firmware  requirements.   See Table 742 for the
       format of the Maxtor Drive Control Page.



                          Table 742
                  Maxtor Drive Control Page


       Bytes two  and three  indicate unique firmware and user
       options.

    XT-4000S Product Specification & OEM Technical Manual
MODE SENSE

       An enable synchronous data transfer request (ESDTR) bit
       of zero  indicates that the target complies with SCSI-2
       for negotiating  a synchronous data transfer.  An ESDTR
       bit of  one indicates  that  following  a  power-on  or
       reset,  the   target  will   not  initiate   the  first
       negotiations for  a synchronous  data  transfer.    The
       default condition is one.

       A  format  data  pattern  enable  (FDPE)  bit  of  zero
       indicates that when byte 2 (format data pattern) in the
       FORMAT UNIT  command contains  00h, the default pattern
       of E5h  is used  for the  format data pattern.  An FDPE
       bit of  one indicates  that the target does not use the
       default pattern.   The data pattern of 00h will be used
       in place of the default pattern.  The default condition
       is zero.

       A contingent  reservation (CR)  bit of  zero  indicates
       that the  target comply  with SCSI-2  and not  set up a
       contingent reservation.  A CR bit of one indicates that
       an "implied reservation" condition is in effect for the
       active initiator  whenever a check condition occurs.  A
       check  condition   will  cause   the  target   to  send
       RESERVATION CONFLICT  status  to  any  other  initiator
       until the  check condition  is addressed  and a RELEASE
       UNIT command  is issued  by the  active initiator  or a
       SCSI bus reset occurs.  The default condition is zero.

       A disable  unit attention  (DUA) bit  of zero indicates
       that the  target complies  with SCSI-2  after reset  or
       power-up.   A DUA  bit of  one indicates that the drive
       will not  issue a  CHECK CONDITION for a UNIT ATTENTION
       condition after  reset or  on power-up.    The  default
       condition is zero.  *

       A START  bit of zero indicates that the target start up
       according to jumpers JP14 and JP38.  A START bit of one
       allows the  drive to  start as soon as power is applied
       regardless of  the jumper  configurations.   Subsequent
       START commands  will be  accepted without  error.   The
       default condition is zero.  *

       A software  selectable ID  (SSID) bit of zero indicates
       that the  drive SCSI  ID is determined by the value set
       by jumpers  JP35, JP36,  and JP37 on the drive PCB.  An
       SSID bit  of one  indicates that  the drive  SCSI ID is
       determined by  the value  of the SCSI address (SCSIADR)
       bits and  the value set by the jumpers will be ignored.
       The default condition is zero.  *

    XT-4000S Product Specification & OEM Technical Manual
                                                    MODE SENSE

       The SCSI  address (SCSIADR)  bits determine the SCSI ID
       if the  SSID bit  is set to one.  The default condition
       is 000b.  *

       Bytes  four  through  seven  are  reserved  for  future
       applications or parameters and are set to zero.

       *These bits  are supported in products that incorporate
       EEPROM.


7.5.10    Read-Ahead Control Parameters Page

       This section  describes  the  read-ahead  control  mode
       parameters supported  by the drive.  The format for the
       read-ahead control  page is  shown in Table 743, Read-
       Ahead Control Parameters (Page Code 38h).




                          Table 743
        Read-Ahead Control Parameters (Page Code 38h)


       If the  read-ahead with  mechanical delay (RAMD) bit is
       set to  one, read-ahead  will not  stop when  a SEEK is
       required.  This includes a SEEK to the next cylinder or
       a SEEK  to an  alternate track.   An  RAMD bit  of zero
       stops read-ahead whenever a SEEK is required.

       A cache  enable (CE)  bit of one enables Read-Ahead.  A
       CE bit of zero disables read-ahead.

       The cache table size field is non-changeable and set to
       0001b.

       The prefetch  threshold field non-changeable and set to
       FFh.   This FFh  value indicates  that  read-ahead  (if
       enabled by  the CE  bit)  is  performed  for  all  READ
       commands, regardless  of  the  transfer  length.    The
       prefetch threshold  field is  the maximum  value of the
       transfer length  (as specified  in the CDB) for which a
       read-ahead operation is performed.

       The maximum  prefetch field  is not  changeable and  is
       reported as  the  number  of  logical  blocks  (at  the
       current block  length) which can be stored in the Read-
       Ahead buffer, which is approximately 45 kilobytes.  The
       maximum prefetch  field is  the maximum  number of data
       blocks which are prefetched by a Read-Ahead operation.

    XT-4000S Product Specification & OEM Technical Manual
MODE SENSE

7.5.11    Error Conditions

       If the  page code  is not  valid, the  drive returns  a
       CHECK CONDITION  status.   The sense  data  is  set  to
       ILLEGAL REQUEST/INVALID FIELD IN CDB (05h/24h).

       If the  drive cannot  read the default information from
       the disk  drive, it terminates the command with a CHECK
       CONDITION status.   The  sense data  is  set  to    NOT
       READY/ILLEGAL FUNCTION FOR DEVICE TYPE (02h/22h).

    XT-4000S Product Specification & OEM Technical Manual
READ
    XT-4000S Product Specification & OEM Technical Manual
                                                          READ


7.6  READ

       The READ  command requests that the drive transfer data
       from the  logical unit to the initiator.  It causes the
       disk drive  to perform an implied SEEK to the cylinder,
       head, and  sector, which  corresponds to  the specified
       LBA.


7.6.1     SCSI Deviations

       There are no deviations.


7.6.2     Command Parameters

       The READ  CDB is formatted as shown in Table 744, READ
       CDB.




                          Table 744
                           READ CDB


       The LBA  field specifies the logical block at which the
       read operation begins.

       The transfer  length  field  specifies  the  number  of
       contiguous logical blocks of data to be transferred.  A
       transfer length  of zero  indicates  that  256  logical
       blocks are transferred.


7.6.3     Error Conditions

       If the  LBA is invalid, or if the LBA plus the transfer
       length results  in an  invalid block  address, the disk
       drive  terminates  the  command  with  CHECK  CONDITION
       status.     The  sense   data   is   set   to   ILLEGAL
       REQUEST/ILLEGAL BLOCK  ADDRESS (05h/21h).   No  data is
       transferred if this condition occurs.

    XT-4000S Product Specification & OEM Technical Manual
READ (EXTENDED)
    XT-4000S Product Specification & OEM Technical Manual
                                               READ (EXTENDED)


7.7  READ (EXTENDED)

       The READ  (EXTENDED) command  requests  that  the  disk
       drive transfer  data  from  the  logical  unit  to  the
       initiator.   It causes  the drive to perform an implied
       SEEK  to   the  cylinder,   head,  and   sector,  which
       corresponds to the specified LBA.


7.7.1     SCSI Deviations

       There are no deviations.


7.7.2     Command Parameters

       The READ  (EXTENDED) CDB is formatted as shown in Table
       745, READ (EXTENDED) CDB.




                          Table 745
                     READ (EXTENDED) CDB


       The LBA  specifies the  logical block at which the read
       operation begins.

       The transfer  length  field  specifies  the  number  of
       contiguous logical blocks of data to be transferred.  A
       transfer length  of zero  indicates  that  no  data  is
       transferred, and is not considered an error by the disk
       drive.


7.7.3     Error Conditions

       If the  LBA is  invalid, and/or  if the  LBA  plus  the
       transfer length  results in  an invalid  block address,
       the  disk  drive  terminates  the  command  with  CHECK
       CONDITION status.   The  sense data  is set  to ILLEGAL
       REQUEST/ILLEGAL BLOCK  ADDRESS (05h/21h).   No  data is
       transferred if this condition occurs.

    XT-4000S Product Specification & OEM Technical Manual
READ BUFFER
    XT-4000S Product Specification & OEM Technical Manual
                                                   READ BUFFER


7.8  READ BUFFER

       The READ BUFFER command is used in conjunction with the
       WRITE BUFFER  command  as  a  diagnostic  function  for
       testing the drive's data buffer memory and the SCSI bus
       integrity.  There is no media access with this command.


7.8.1     SCSI Deviations

       There are no deviations.


7.8.2     Command Parameters

       The READ  BUFFER CDB  is formatted  as shown  in  Table
       746, READ BUFFER CDB.




                          Table 746
                       READ BUFFER CDB


       The function  of this command and the meaning of fields
       within the  command  descriptor  block  depend  on  the
       contents of  the mode  field.   The drive only supports
       the combined header and data mode (000b).

       The allocation  length field  specifies the  number  of
       bytes the  initiator has  allocated  for  the  returned
       buffer data.   An  allocation length  of  zero  is  not
       considered an  error by  the drive, and no data is sent
       to the  initiator.   The initiator  may request  up  to
       65,535 bytes  to be  transferred, including  the 4 byte
       header.   If the  number of bytes requested exceeds the
       drive buffer  size,  the  drive  transfers  the  entire
       buffer and  terminates the  command without  an  error.
       Under this  condition, the  initiator  must  check  the
       value in  the available length field in the READ BUFFER
       header  (see   Table  747,   READ  BUFFER  Header)  to
       determine the number of bytes returned.


7.8.3     Command Usage

       It is  recommended that the initiator issue the RESERVE
       UNIT command  before it issues the READ BUFFER command,
       to ensure  that no  other initiator  sends data  to the

    XT-4000S Product Specification & OEM Technical Manual
READ BUFFER

       drive's data  buffer. After the drive has completed the
       READ BUFFER  command, the  initiator issues  a  RELEASE
       UNIT command to release the drive.

       To determine  the maximum  amount of  data that  can be
       transferred with  the  READ  BUFFER  and  WRITE  BUFFER
       commands, the initiator can issue a READ BUFFER command
       with the  allocation length  set to  four.  This causes
       the drive to return only the READ BUFFER header.  Bytes
       one through  three of  the header  contain the  maximum
       buffer size.


7.8.4     Data Format

       The combined  header and data mode utilizes a four-byte
       header followed  by the  data bytes.   In this mode the
       buffer ID  and the  buffer offset  fields are reserved.
       See Table 747, READ BUFFER Header.




                          Table 747
                      READ BUFFER Header


       The available  length field  specifies the total number
       of data  bytes that  are available in the target's data
       buffer.   This number  is not  reduced to  reflect  the
       allocation length  nor is  it reduced  to  reflect  the
       actual number  of bytes  written using the WRITE BUFFER
       command.   Following the READ BUFFER header, the target
       shall transfer  data from  its data buffer.  The target
       terminates the  DATA IN  phase when  allocation  length
       bytes of header plus data have been transferred or when
       all  available   header  and   buffer  data  have  been
       transferred to the initiator, whichever is less

7.8.5     Error Conditions

       If the  data in  the buffer has been modified since the
       last WRITE  BUFFER command  was issued,  or if no WRITE
       BUFFER command  has been  issued since  the last  RESET
       condition, the READ BUFFER command is terminated with a
       CHECK CONDITION  status and  a MISCOMPARE/Compare Error
       (0Eh/1Dh) sense  key/error code.    If  the  allocation
       length is  set to  four or  less, the  drive  does  not
       return this error.

    XT-4000S Product Specification & OEM Technical Manual
READ CAPACITY
    XT-4000S Product Specification & OEM Technical Manual
                                                 READ CAPACITY


7.9  READ CAPACITY

       The READ  CAPACITY command  is used  to  determine  the
       maximum logical  block number  which can be accessed by
       the initiator.   This  command also returns the size of
       the logical  block.  The information is returned to the
       initiator during the DATA IN phase.

       In addition, the command is used to determine whether a
       file of  a given  size will  fit  within  a  physically
       contiguous space,  by requesting  the number  of blocks
       past a  specified block  before a  substantial delay is
       encountered (i.e., a cylinder boundary).


7.9.1     SCSI Deviations

       There are no deviations.


7.9.2     Command Parameters

       The READ  CAPACITY CDB  is formatted  as shown in Table
       748, READ CAPACITY CDB.




                          Table 748
                      READ CAPACITY CDB


       The LBA  field is  only used  when the  partial  medium
       indicator  (PMI)  bit  is  set  to  one.    This  field
       specifies the  block address  to use when computing the
       last block before a substantial delay is encountered.

       A partial  medium indicator  (PMI) bit of one indicates
       that the  information returned  is for  the  last  full
       logical block  (from the  block specified  in  the  LBA
       field) which  can be  transferred before  a substantial
       delay is  encountered (i.e.,  a cylinder  boundary).  A
       partial medium  indicator (PMI)  bit of  zero indicates
       that the  information returned  is for the last logical
       block of the disk drive.

    XT-4000S Product Specification & OEM Technical Manual
READ CAPACITY

7.9.3     Data Format

       The 8  bytes of  READ CAPACITY  data  is  sent  to  the
       initiator during  the DATA IN phase and is formatted as
       shown in Table 749, READ CAPACITY Data Format.




                          Table 749
                  READ CAPACITY Data Format


       The LBA  field specifies  the last logical block on the
       unit (if  the partial  medium indicator  (PMI)  bit  is
       zero),  or   the  last  full  logical  block  before  a
       substantial delay is encountered (if the partial medium
       indicator (PMI) bit is one).

       The block  length  field  specifies  the  size  of  the
       logical block, in bytes.


7.9.4     Error Conditions

       If the  partial medium  indicator (PMI) bit is one, and
       the LBA  is invalid,  the  disk  drive  terminates  the
       command with CHECK CONDITION status.  The sense data is
       set to ILLEGAL REQUEST/ILLEGAL BLOCK ADDRESS (05h/21h).

       If the  partial medium  indicator (PMI) bit is zero and
       the LBA  is not  zero, the  disk drive  terminates  the
       command with CHECK CONDITION status.  The sense data is
       set to ILLEGAL REQUEST/INVALID FIELD IN CDB (05h/24h).

    XT-4000S Product Specification & OEM Technical Manual
READ DEFECT LIST
    XT-4000S Product Specification & OEM Technical Manual
                                              READ DEFECT LIST


7.10 READ DEFECT LIST

       The READ  DEFECT LIST  command requests  that the drive
       transfer one  or more of the defect lists maintained by
       the drive  to the initiator.  The initiator may request
       the original P list, the G list, or both.


7.10.1    SCSI Deviations

       There are no deviations.


7.10.2    Command Parameters

       The READ DEFECT LIST CDB is formatted as shown in Table
       750, READ DEFECT LIST CDB.




                          Table 750
                     READ DEFECT LIST CDB

       A P list bit of one specifies that the P list should be
       returned by  the drive  during the  DATA IN  phase.  To
       request both  lists, this bit may be set in combination
       with the G list bit.

       A G  list bit  of one, specifies that the G list should
       be returned  by the drive during the DATA IN phase.  To
       request both  lists, this bit may be set in combination
       with the  P list bit.  A request by the initiator for a
       G list  to a drive that has no entries in the G list is
       not considered an error; instead the drive returns only
       the P list, if also requested, or if only the G list is
       requested, the  4 byte  header, with  the  defect  list
       length field set to zero.

       When both  the P  and G  list bits  are set to one, the
       drive returns  both lists.  The drive sends the list in
       ascending order, and merges the lists.  When both the P
       and G list bits are set to zero, the disk drive returns
       only the defect list header.

       The defect  list format  field,  byte  one,  bits  zero
       through two,  specifies  the  format  of  the  returned
       defect list.   Table 751, READ DEFECT LIST Defect List

    XT-4000S Product Specification & OEM Technical Manual
READ DEFECT LIST

       Formats, lists  the types  of formats  supported by the
       disk drive.

       NOTE: The initiator  should use  the  drive's  internal
       defect maps, rather than sending a D list to the drive.
       Maxtor performs  extensive testing  of all  drives, and
       adds all  areas of defective or marginal performance to
       the defect  lists.    If  the  initiator  disables  the
       internal lists  using the  disable primary  (DPRY) bit,
       marginal sectors  might  cause  future  loss  of  data.
       Also,  the   drive  uses  sophisticated  algorithms  to
       determine when  to deallocate  multiple sectors  for  a
       single defect.  The limitations of the bytes from index
       format of  the  READ  DEFECT  LIST  and    FORMAT  UNIT
       commands do  not allow  for reporting  the length  of a
       defect, even though this information is stored in the P
       list.   Therefore, the  drive is  better able  to judge
       when a  defect will cross sector boundaries than is the
       initiator.




                          Table 751
             READ DEFECT LIST Defect List Formats


       The allocation  length field  specifies the  number  of
       bytes the  initiator has  allocated  for  the  returned
       defect list.   The  drive terminates  the DATA IN phase
       when  the  number  of  bytes  transferred  reaches  the
       allocation length  field value, or when the entire list
       has been transferred, whichever is less.


7.10.3    Header
       The defect  list header  (see Table  752, READ  DEFECT
       LIST Header)  is transferred  from  the  drive  to  the
       initiator during  the DATA  IN phase of the READ DEFECT
       LIST command.   The defect list header is 4 bytes long,
       followed by  zero or  more  defect  descriptors.    The
       header specifies  the format  and the  total number  of
       bytes in the returned defect list.




                          Table 752
                   READ DEFECT LIST Header

    XT-4000S Product Specification & OEM Technical Manual
                                              READ DEFECT LIST

       A P  list bit  of one  indicates that the drive returns
       the P  list during  the DATA IN phase.  This bit may be
       set in combination with the G list bit.

       A G  list bit  of one  indicates that the drive returns
       the G  list during  the DATA IN phase.  This bit may be
       set in combination with the P list bit.

       The defect  list format  field specifies  the format of
       the returned defect list.

       The defect list length field specifies the total number
       of bytes  (not the  total number of defect descriptors)
       in the defect list.  This length does not include the 4
       bytes in the header.

       The defect  descriptors are  in ascending  order.   For
       determining ascending  order, the  cylinder  number  of
       defect is  considered the  most significant part of the
       address,  and  the  defect  bytes  from  index/physical
       sector is  considered the least significant part of the
       address.


7.10.4    Block Format

       When the  block address format is specified, the defect
       list transferred to the initiator from the drive during
       the DATA  IN phase is formatted as shown in Table 753,
       READ DEFECT LIST Defect Descriptor(s), Block Format.

       NOTE:  This format is not recommended.




                          Table 753
     READ DEFECT LIST Defect Descriptor(s), Block Format


       The defect list format field is set to zero to indicate
       that the list is in block format.

       The defect  list  block  address  field  specifies  the
       address of the block that contains the defect.

       Each  defect  descriptor  for  the  block  format  mode
       specifies a  4 byte  block address  that  contains  the
       defect.

    XT-4000S Product Specification & OEM Technical Manual
READ DEFECT LIST

7.10.5    Bytes from Index Format

       When the  bytes from  index format  is  specified,  the
       defect list,  transferred to  the  initiator  from  the
       drive during  the DATA  IN phase, is formatted as shown
       in Table  754, READ  DEFECT LIST Defect Descriptor(s),
       Bytes from Index Format.




                          Table 754
READ DEFECT LIST Defect Descriptor(s), Bytes from Index Format


       The defect  list format  is set to 04h to indicate that
       the list is in bytes from index format.

       The cylinder  number  of  defect  field  specifies  the
       physical cylinder number which contains the defect.

       The head  number of  defect field  specifies  the  head
       number which contains the defect.

       The defect  bytes from index field specifies the number
       of bytes  between the  index  and  the  defect  on  the
       specified track.   A  value of  FFFFFFFFh in  the bytes
       from index  field indicates  that the  entire track  is
       reassigned.


7.10.6    Physical Sector Format

       When the  physical  sector  format  is  specified,  the
       defect list,  transferred to  the  initiator  from  the
       drive during  the DATA  IN phase, is formatted as shown
       In Table  755, READ  DEFECT LIST Defect Descriptor(s),
       Physical Sector Format.




                          Table 755
READ DEFECT LIST Defect Descriptor(s), Physical Sector Format


       The defect  list format field is set to 05h to indicate
       the list is in physical sector format.

       The cylinder  number  of  defect  field  specifies  the
       cylinder number which contains the defect.

    XT-4000S Product Specification & OEM Technical Manual
                                              READ DEFECT LIST

       The head  number of  defect field  specifies  the  head
       number which contains the defect.

       The defect  sector number  field specifies  the  sector
       number which  contains the  defect.   A  defect  sector
       number of FFFFFFFFh indicates that the entire track was
       reassigned.


7.10.7    Error Conditions

       If the  preferred defect  list format  does not specify
       block, bytes  from index,  or physical format, the disk
       drive  terminates  the  command  with  CHECK  CONDITION
       status.   The    sense   data   is   set   to   ILLEGAL
       REQUEST/INVALID FIELD IN CDB (05h/24h).

    XT-4000S Product Specification & OEM Technical Manual
READ LONG
    XT-4000S Product Specification & OEM Technical Manual
                                                     READ LONG


7.11 READ LONG

       The READ  LONG command  requests the drive to perform a
       read operation  of one  data block  and the 6 ECC bytes
       associated with that block. The data from the block and
       the ECC  bytes are  transferred to the initiator during
       the DATA IN phase.

       NOTE: The READ  LONG command  does not  perform any ECC
       correction when reading the disk.


7.11.1    SCSI Deviations

       The disk  drive recognizes  either E8h  or 3Eh as being
       the READ  LONG command.   Maxtor implemented E8h before
       the SCSI-2 definition of 3Eh.  The E8h form is a vendor
       unique  command,  and  thus  is  outside  of  the  SCSI
       standard.   The 3Eh  form of the command is the defined
       SCSI-2 version of the READ LONG command.

       The Maxtor  vendor unique  definition differs  from the
       SCSI-2 definition  in that  Maxtor (E8h)  defines bytes
       seven and  eight of  the CDB  as always  equal to zero,
       and the  transfer length is always one sector (plus the
       ECC bytes).   The  E8h command  does  not  support  the
       CORRCT bit in byte one.


7.11.2    Command Parameters

       The READ  LONG CDB is formatted as shown in Table 756,
       READ LONG CDB.




                          Table 756
                        READ LONG CDB


       The block  address field  specifies the  block at which
       the read long operation begins.

       CAUTION:     The physical location of the READ LONG and
       WRITE LONG  block address  is always computed using the
       physical sector size instead of the logical block size.

    XT-4000S Product Specification & OEM Technical Manual
                                                     READ LONG

7.11.3    Error Conditions

       If the  block address  is invalid, the drive terminates
       the command  with CHECK  CONDITION status.   The  sense
       data is  set to  ILLEGAL REQUEST/ILLEGAL  BLOCK ADDRESS
       (05h/21h).

    XT-4000S Product Specification & OEM Technical Manual
READ LONG (SCSI-2)
    XT-4000S Product Specification & OEM Technical Manual
                                            READ LONG (SCSI-2)


7.12 READ LONG (SCSI-2)

       The READ LONG command  requests that the drive transfer
       data to the initiator.  The data passed during the READ
       LONG command  includes the data bytes and the ECC bytes
       recorded on  the medium.   The most recent data written
       in the  addressed logical block is returned.  See Table
       757, READ LONG Command.




                          Table 757
                      READ LONG Command


       A corrected (CORRCT) bit of zero causes a logical block
       to be  read without  any correction made by the target.
       A CORRCT  bit of one causes the data to be corrected by
       ECC before being transferred to the initiator.

       The logical  block address  field specifies the logical
       block to be read.

       The byte  transfer length  field must specify the exact
       number of  bytes of  data to be transferred.  If a non-
       zero byte  transfer length  does not  exactly match the
       available data length, the drive terminates the command
       with CHECK  CONDITION status.  The sense data is set to
       ILLEGAL REQUEST/INVALID  FIELD IN  CDB.   The valid and
       ILI bits  are set  to one  and the information field is
       set to the difference of the requested length minus the
       actual length  in bytes.  Negative values are indicated
       by two's complement notation.

    XT-4000S Product Specification & OEM Technical Manual
READ MANUFACTURERS DEFECT LIST
    XT-4000S Product Specification & OEM Technical Manual
                                READ MANUFACTURERS DEFECT LIST


7.13 READ MANUFACTURERS DEFECT LIST

       The READ  MANUFACTURERS DEFECT  LIST returns  a list of
       defects recorded  by the  manufacturer for  the  drive.
       The data is returned in the format shown in Table 759,
       READ MANUFACTURERS  DEFECT  LIST    Defect  Descriptors
       Returned Format.

       The defect  descriptor is repeated once for each defect
       reported.

7.13.1    SCSI Deviations

       This implementation is vendor unique.


7.13.2    Command Parameters

       The READ  MANUFACTURERS DEFECT LIST CDB is formatted as
       shown in Table 758.




                          Table 758
              READ MANUFACTURERS DEFECT LIST CDB



7.13.3    Data Format

       The defect  descriptor(s) returned  is shown  in  Table
       759.




                          Table 759
  READ MANUFACTURERS DEFECT LIST Defect Descriptors Returned
                            Format

    XT-4000S Product Specification & OEM Technical Manual
REASSIGN BLOCK
    XT-4000S Product Specification & OEM Technical Manual
                                                REASSIGN BLOCK


7.14 REASSIGN BLOCK

       The REASSIGN  BLOCK command  requests  that  the  drive
       relocate a  logical block(s)  from a defective physical
       sector(s) to a physical sector(s) without defect.

       During the  DATA OUT  phase, the  initiator transfers a
       defect list  that contains  the logical  block(s) to be
       reassigned.   The drive  reassigns the  media used  for
       each logical  block specified  by the  initiator.   The
       data  contained   in  those  blocks  specified  by  the
       initiator may  be altered,  but the  data in  all other
       blocks is preserved.

       During the  reassign operation,  if all available spare
       sectors within  a zone  (see 7.4.6  Format Device  Page
       (MODE SELECT),  or 7.5.6  Direct-Access  Device  Format
       Parameters Page  (MODE SENSE)  earlier in this chapter)
       become  allocated,   the  entire  track  is  marked  as
       defective in  the G  list, and  an alternate  track  is
       used.   The disk  drive moves  all data  blocks on  the
       track to the alternate track.  If all the spare sectors
       on an  alternate track  have been  used, the  alternate
       track is relocated to another alternate track.

       Successful  completion  of  a  REASSIGN  BLOCK  command
       results in one or more new entries in the G list.

7.14.1    SCSI Deviations

       There are no deviations.


7.14.2    Command Parameters

       The REASSIGN  BLOCK CDB  is formatted as shown in Table
       760, REASSIGN BLOCK CDB.




                          Table 760
                      REASSIGN BLOCK CDB

    XT-4000S Product Specification & OEM Technical Manual
                                                REASSIGN BLOCK

7.14.3    Defect List Format

       The REASSIGN  BLOCK parameter list consists of a 4 byte
       header (Table 761, REASSIGN BLOCK Defect List Header),
       which contains the defect list length, followed by zero
       or  more  defect  descriptors.    The  length  of  each
       descriptor is 4 bytes.  This information is transferred
       from the  initiator to  the drive  during the  DATA OUT
       phase of the REASSIGN BLOCK command.




                          Table 761
              REASSIGN BLOCK Defect List Header


       The  defect  list  length  field  specifies  the  total
       length,  in  bytes,  of  the  defect  descriptors  that
       follow.   The length  is equal to four times the number
       of defect descriptors.  A defect list length of zero is
       not considered an error by the drive.

       The defect  descriptor contains  the 4  byte defect LBA
       (see Table  762, REASSIGN  BLOCK Defect Descriptor(s))
       that specifies  the location of the defect.  The defect
       descriptors must be in ascending order.




                          Table 762
             REASSIGN BLOCK Defect Descriptor(s)



7.14.4    Error Conditions

       If the  drive has insufficient capacity to reassign all
       the defective  blocks, the drive terminates the command
       with CHECK  CONDITION status.  The sense data is set to
       MEDIUM  ERROR/NO   DEFECT  SPARE   LOCATION   AVAILABLE
       (03h/32h).

       If the  defect LBA is invalid, the drive terminates the
       command with CHECK CONDITION status.  The sense data is
       set to ILLEGAL REQUEST/ILLEGAL BLOCK ADDRESS (05h/21h).

    XT-4000S Product Specification & OEM Technical Manual
RECEIVE DIAGNOSTIC RESULTS
    XT-4000S Product Specification & OEM Technical Manual
                                    RECEIVE DIAGNOSTIC RESULTS


7.15 RECEIVE DIAGNOSTIC RESULTS

       The  RECEIVE   DIAGNOSTIC  RESULTS   command   requests
       analysis data be sent to the initiator after completion
       of a SEND DIAGNOSTIC command.


7.15.1    SCSI Deviations

       There are no deviations.


7.15.2    Command Parameters

       The RECEIVE  DIAGNOSTIC RESULTS  CDB  is  formatted  as
       shown in Table 763, RECEIVE DIAGNOSTIC RESULTS CDB.




                          Table 763
                RECEIVE DIAGNOSTIC RESULTS CDB


       The allocation  length field  specifies the  number  of
       bytes that the initiator has allocated for the returned
       diagnostic  data.     An   allocation  length  of  zero
       indicates that  no diagnostic  data is  returned.   Any
       other value  indicates the  maximum number of bytes the
       drive transfers.  The data transfer terminates when the
       number of  bytes in  the  allocation  length  has  been
       transferred, or  when all the available diagnostic data
       has been transferred, whichever is less.

       See 7.22  SEND DIAGNOSTIC  later in this chapter, for a
       description of data sent to the initiator from the disk
       drive during  the DATA IN phase of a RECEIVE DIAGNOSTIC
       RESULTS command.


7.15.3    Data Format

       See 7.22 SEND DIAGNOSTIC later in this chapter.


7.15.4    Error Conditions

       If  the  RECEIVE  DIAGNOSTIC  RESULTS  command  is  not
       preceded by  a SEND  DIAGNOSTIC command, the disk drive
       terminates the  command with  CHECK  CONDITION  status.

    XT-4000S Product Specification & OEM Technical Manual
                                    RECEIVE DIAGNOSTIC RESULTS

       The  sense  data  is  set  to  ILLEGAL  REQUEST/INVALID
       COMMAND (05h/20h).

    XT-4000S Product Specification & OEM Technical Manual
RELEASE UNIT
    XT-4000S Product Specification & OEM Technical Manual
                                                  RELEASE UNIT


7.16 RELEASE UNIT

       The RELEASE  UNIT command  causes the drive (previously
       reserved by  the RESERVE  UNIT command) to be released.
       Once  the   RELEASE  UNIT   command  is  issued,  other
       initiators can access the disk drive.

       It is not an error to release a disk drive which is not
       currently reserved.

       An initiator  that  holds  a  current  reservation  may
       modify that reservation by issuing another RELEASE UNIT
       command.  The superseding RELEASE UNIT command releases
       the previous  reservation when  the new  reservation is
       granted.   The previous  reservation is not modified if
       the new  reservation cannot  be granted,  and the drive
       returns a RESERVATION CONFLICT status.


7.16.1    SCSI Deviations

       The disk  drive does  not support  the  extent  release
       option.


7.16.2    Command Parameters

       The RELEASE  UNIT CDB  is formatted  as shown  in Table
       764, RELEASE UNIT CDB.




                          Table 764
                       RELEASE UNIT CDB


       If the  third party  reservation (3rdPty) bit is set to
       one, the  drive is  released,  provided  the  following
       conditions are true:

         The unit  was originally  reserved using  the  third
          party option in the RESERVE UNIT command.

         The same  initiator that  issued  the  RESERVE  UNIT
          command is requesting the release of the drive.

         The initiator  specifies the same SCSI bus device ID
          in the third party ID field as was specified in that
          field by the initiator in the RESERVE UNIT command.

    XT-4000S Product Specification & OEM Technical Manual
                                                  RELEASE UNIT

       The third  party device ID field specifies the SCSI bus
       device ID for which the drive was reserved.


7.16.3    Error Conditions

       If the extent reservation option is specified, the disk
       drive  terminates  the  command  with  CHECK  CONDITION
       status.     The  sense   data   is   set   to   ILLEGAL
       REQUEST/INVALID FIELD IN CDB (05h/24h).

       If the third party release option is specified, and the
       unit was  not originally  reserved with the third party
       option, the  disk drive  terminates  the  command  with
       CHECK CONDITION  status.   The sense  data  is  set  to
       ILLEGAL REQUEST/INVALID FIELD IN CDB (05h/24h).

       If the third party release option is specified, and the
       third party  device ID  is not  the  same  as  the  one
       specified in  the original  RESERVE UNIT  command,  the
       drive  terminates  the  command  with  CHECK  CONDITION
       status.     The  sense   data   is   set   to   ILLEGAL
       REQUEST/INVALID FIELD IN CDB (05h/24h).

       If the third party release option is specified, and the
       initiator SCSI  ID is  not the  same  as  that  of  the
       initiator which originally reserved the unit, the drive
       terminates the  command  with  a  RESERVATION  CONFLICT
       status.

    XT-4000S Product Specification & OEM Technical Manual
REQUEST SENSE
    XT-4000S Product Specification & OEM Technical Manual
                                                 REQUEST SENSE


7.17 REQUEST SENSE

       The REQUEST  SENSE command  provides a  means  for  the
       initiator to  obtain more  detailed  information  after
       execution of  a command.   Typically,  a REQUEST  SENSE
       command is issued if the previous command has completed
       with  a   CHECK  CONDITION   status  returned   to  the
       initiator.

       An initiator  should issue  a REQUEST  SENSE command as
       soon as  it receives a CHECK CONDITION status to obtain
       the sense  data saved  by the drive.  The initiator can
       issue several  REQUEST SENSE  commands at  this time to
       obtain  the   extended  sense  data,  as  well  as  the
       nonextended  sense  data.    However,  when  the  drive
       receives a command other than a REQUEST SENSE the drive
       clears the sense data for the previous command.

       Although Maxtor  supports the nonextended sense format,
       it is  not recommended  that this format be used in any
       future products.   All  new development  should use the
       extended sense  format, and  the sense  key, to process
       any errors.


7.17.1    SCSI Deviations

       There are no deviations.


7.17.2    Command Parameters

       The REQUEST  SENSE CDB  is formatted  as shown in Table
       765, REQUEST SENSE CDB.



                          Table 765
                      REQUEST SENSE CDB


       The allocation  length field  specifies the  number  of
       bytes of data the initiator has allocated for the sense
       information.   The drive transfers sense data until the
       allocation length  is exhausted,  or until  all of  the
       sense data  has been  transferred, whichever  is  less.
       The  count   supplied  determines  the  format  of  the
       returned sense  data, as  explained  in  the  following
       subsection.

    XT-4000S Product Specification & OEM Technical Manual
                                                 REQUEST SENSE

7.17.3    Data Format

       The format  of the  returned sense  data depends on the
       number of  bytes specified  in  the  allocation  length
       field  of   the  CDB.    Two  sense  data  formats  are
       supported:

         An allocation  length of  zero results in a transfer
          of 4 bytes in the nonextended sense data format.

         An allocation  length greater than zero results in a
          transfer of  up to  the requested  number  of  sense
          bytes,  or   until  all  the  sense  data  has  been
          transferred, in the extended sense data format.


A    NONEXTENDED SENSE DATA FORMAT

       When the  allocation length  is zero,  the  disk  drive
       returns the  nonextended sense  data for  all  commands
       (see Table  766, REQUEST  SENSE Nonextended Sense Data
       Format).

       Although Maxtor  supports the  nonextended  sense  data
       format, it  is not recommended that this format be used
       in any future products.  All new development should use
       the extended  sense data  format, and the sense key, to
       process any errors.




                          Table 766
         REQUEST SENSE Nonextended Sense Data Format


       When set,  the valid  bit indicates  that the LBA field
       contains  valid   information  related   to  the  error
       condition.

       The LBA  field specifies  the LBA  associated with  the
       error class  and error  code.    For  the  FORMAT  UNIT
       command, these  bytes can be either logical or physical
       block addresses,  depending on the format specified for
       the defect list.

       Together, the  error class  field and  the  error  code
       field  are   called  the  nonextended  sense  code  and
       indicate the  type of  error that occurred.  (See Table
       772, Additional Sense Codes.)

    XT-4000S Product Specification & OEM Technical Manual
REQUEST SENSE

B    EXTENDED SENSE DATA FORMAT

       The extended  sense data  format is  available for  all
       commands,  and  is  returned  by  the  drive  when  the
       allocation  length   specified  in  the  REQUEST  SENSE
       command is  greater  than  0  bytes  (see  Table  767,
       Extended Sense Data Format).




                          Table 767
                  Extended Sense Data Format


       A valid  bit of  one indicates  the  information  field
       contains  valid   information  related   to  the  error
       condition.

       The error  code field indicates the type of error being
       reported.   The drive supports the reporting of current
       errors.

       The segment  number field is not supported by the drive
       and is returned as zero.

       The incorrect length indicator (ILI) bit indicates that
       the data  available in  the buffer  is greater than the
       allocation length specified in the READ BUFFER command.

       The sense  key, additional  sense code  and  additional
       sense code  qualifier provide  information relating  to
       the error  and exception  conditions.   The  sense  key
       definitions are given in Table 772.

       The  contents  of  the  information  field  is  command
       specific and is valid only if the valid bit is one.

       The additional  sense length field indicates the number
       of additional sense bytes to follow.  If the allocation
       length of  the command descriptor block is too small to
       transfer  all   of  the  additional  sense  bytes,  the
       additional sense  length is not adjusted to reflect the
       truncation.

       The  command-specific  information  field  may  contain
       information following  a REASSIGN  BLOCKS command  that
       fails.

       The additional  sense code  definitions  are  given  in
       Table 772.   If the condition is not reportable by the

    XT-4000S Product Specification & OEM Technical Manual
                                                 REQUEST SENSE

       drive,  the   additional  sense   code  is  set  to  NO
       ADDITIONAL SENSE INFORMATION.

       The additional  sense code  qualifier  definitions  are
       given in  Table 772.   If  the error  condition is not
       reportable by  the drive,  the  additional  sense  code
       qualifier  should   be  set   to  NO  ADDITIONAL  SENSE
       INFORMATION.

       The field replaceable unit code is not supported by the
       drive is returned as zero.

       The sense-key specific field is valid when the value of
       the sense-key  specific valid  (SKSV) bit  is one.  The
       definition of  this field is determined by the value of
       the sense  key field.  This field is reserved for sense
       keys  not  described  below.    An  SKSV  bit  of  zero
       indicates  that  this  field  does  not  contain  valid
       information.

       If the sense key is ILLEGAL REQUEST and the SKSV bit is
       one these fields point to illegal parameters in command
       descriptor blocks and data parameters.  These sense-key
       specific fields are defined in Table 768.




                          Table 768
                     Field Pointer Bytes


       A command  data (C/D)  bit of  one indicates  that  the
       illegal parameter  is in  the command descriptor block.
       A C/D  bit of zero indicates that the illegal parameter
       is in  the data parameters sent by the initiator during
       the DATA OUT phase.

       A bit  pointer valid  (BPV) bit  of zero indicates that
       the value in the bit pointer field is not valid.  A BPV
       bit  of  one  indicates  that  the  bit  pointer  field
       specifies which bit of the byte designated by the field
       pointer field  is in  error.  When a multiple-bit field
       is in  error, the bit pointer field points to the most-
       significant (left-most) bit of the field.

       The field  pointer field  indicates which  byte of  the
       command descriptor  block or  of the parameter data was
       in error.   Bytes  are numbered  starting from zero, as
       shown  in   the  tables  describing  the  commands  and
       parameters.   When a  multiple-byte field  is in error,

    XT-4000S Product Specification & OEM Technical Manual
REQUEST SENSE

       the pointer points to the most- significant (left-most)
       byte of the field.

       If the  sense key is RECOVERED ERROR, HARDWARE ERROR or
       MEDIUM ERROR  and if the SKSV bit is one, the sense-key
       specific fields  identify the  actual number of retries
       used in attempting to recover from the error condition.
       These fields are defined in Table 769.




                          Table 769
                   Actual Retry Count Bytes


       The actual retry count field returns information on the
       actual number  of retries used in attempting to recover
       an error or exception condition.

       If the  sense key is NOT READY and the SKSV bit is one,
       the sense-key specific these fields are defined for the
       FORMAT UNIT  command with  the Immed  bit set  to  one.
       These fields are defined in Table 770.




                          Table 770
               Format Progress Indication Bytes


       The progress  indication field  is a  percent  complete
       indication in which the returned value is the numerator
       that has  65536  (10000h)  as  its  denominator.    The
       progress indication  is based  upon  the  total  format
       operation including any certification or initialization
       operations.

       The sense  key field indicates status information about
       any errors  detected during  the operation.  The errors
       are listed  and defined  in Table  771, REQUEST  SENSE
       Extended Sense Key Codes.




                          Table 771
            REQUEST SENSE Extended Sense Key Codes

    XT-4000S Product Specification & OEM Technical Manual
                                                 REQUEST SENSE

C    SENSE CODES

       Table 772, Additional Sense Codes, lists and describes
       the sense codes supported by the disk drive.




                          Table 772
                    Additional Sense Codes





                     Table 772 (cont'd)
                    Additional Sense Codes





                     Table 772 (cont'd)
                    Additional Sense Codes



7.17.4    Error Conditions

       If a  CHECK CONDITION  status is  received on a REQUEST
       SENSE command, any sense data returned by the target is
       invalid.

    XT-4000S Product Specification & OEM Technical Manual
RESERVE UNIT
    XT-4000S Product Specification & OEM Technical Manual
                                                  RESERVE UNIT


7.18 RESERVE UNIT

       The  RESERVE  UNIT  command  is  used  to  reserve  the
       specified drive for exclusive use by the initiator or a
       designated third  party.   This reservation  remains in
       effect until  one of  the following conditions releases
       the reservation:

         a RELEASE  UNIT command  from the  same initiator is
       received by the drive.
         a BUS  DEVICE RESET message is received by the drive
       from any initiator.
         a SCSI BUS RESET occurs.

       If a  RESERVE UNIT  command, or  any other  command, is
       received for  a drive  which  is  reserved  by  another
       initiator,  the   drive  returns  RESERVATION  CONFLICT
       status.

       An initiator  that  holds  a  current  reservation  may
       modify that reservation by issuing another RESERVE UNIT
       command.  The superseding RESERVE UNIT command releases
       the previous  reservation when  the new  reservation is
       granted.   The previous  reservation is not modified if
       the new  reservation cannot  be granted,  and the drive
       returns RESERVATION CONFLICT status.


7.18.1    SCSI Deviations

       The disk  drive does not support the extent reservation
       option.

       The disk  drive does  not support  reservation queuing.
       If a  RESERVE UNIT  command is  received for  a logical
       unit  which   is  already   reserved  for  a  different
       initiator,  the   drive  returns  RESERVATION  CONFLICT
       status.


7.18.2    Command Parameters

       The RESERVE  UNIT CDB  is formatted  as shown  in Table
       773, RESERVE UNIT CDB.




                          Table 773
                       RESERVE UNIT CDB

    XT-4000S Product Specification & OEM Technical Manual
                                                  RESERVE UNIT

       The third  party reservation  (3rdPty)  bit  allows  an
       initiator to reserve a disk drive for another device on
       the SCSI  bus.  If the third party reservation (3rdPty)
       bit is  set to  one, an initiator is allowed to reserve
       the specified  drive for  the SCSI bus device specified
       in the  third party device ID field, byte one, bits one
       through three.   This  option is  intended for  use  in
       multiple-initiator systems.   Any  device that uses the
       third party reservation option to reserve must also use
       the third party reservation option to release (see 7.16
       RELEASE UNIT  earlier in this chapter) before any other
       commands can be sent.

       The third  party device ID field specifies the SCSI bus
       device ID  of the  device being  reserved.   The ID  is
       valid only  when the third party reservation bit is set
       to one.

       The extent  bit is  not supported  and must  be set  to
       zero.

       The reservation  identification field  is not supported
       and must be set to zero.

       The extent  list length field is not supported and must
       be set to zero.


7.18.3    Error Conditions

       If the  extent, reservation  identification, or  extent
       list length  fields are  not zero, the drive terminates
       the command  with  a  CHECK  CONDITION  status  and  an
       ILLEGAL REQUEST/Invalid  Field in  CDB (05h/24h)  sense
       key/error code.

    XT-4000S Product Specification & OEM Technical Manual
REZERO UNIT
    XT-4000S Product Specification & OEM Technical Manual
                                                   REZERO UNIT


7.19 REZERO UNIT

       The REZERO UNIT command requests that the drive set the
       logical unit to cylinder zero.


7.19.1    SCSI Deviations

       There are no deviations.


7.19.2    Command Parameters

       The REZERO  UNIT CDB  is formatted  as shown  in  Table
       774, REZERO UNIT CDB.




                          Table 774
                       REZERO UNIT CDB

    XT-4000S Product Specification & OEM Technical Manual
SEEK
    XT-4000S Product Specification & OEM Technical Manual
                                                          SEEK

7.20 SEEK

       The SEEK  command causes  the disk drive to SEEK to the
       cylinder of  the specified  logical block location.  If
       the  logical  block  number  specifies  a  block  on  a
       defective track, the SEEK to the alternate track is not
       performed until  the drive  receives  and  processes  a
       command which accesses the media.


7.20.1    SCSI Deviations

       There are no deviations.


7.20.2    Command Parameters

       The SEEK  CDB is formatted as shown in Table 775, SEEK
       CDB.




                          Table 775
                           SEEK CDB


       The LBA  field specifies  the LBA to seek to.  When the
       SEEK  command   completes  without   any  errors,   the
       read/write heads  are positioned at the cylinder of the
       specified block address.


7.20.3    Error Conditions

       If  the   LBA  is  invalid,  the  drive  returns  CHECK
       CONDITION status.   The  sense data  is set to  ILLEGAL
       REQUEST/ILLEGAL BLOCK ADDRESS (05h/21h).

    XT-4000S Product Specification & OEM Technical Manual
SEEK (EXTENDED)
    XT-4000S Product Specification & OEM Technical Manual
                                               SEEK (EXTENDED)


7.21 SEEK (EXTENDED)

       The SEEK  (EXTENDED) command  causes the  disk drive to
       SEEK to  the cylinder  of the  specified logical  block
       location.   If the  logical block  number  specifies  a
       block on  a defective  track, the SEEK to the alternate
       track is  not performed  until the  drive receives  and
       processes a command which accesses the media.


7.21.1    SCSI Deviations

       There are no deviations.


7.21.2    Command Parameters

       The SEEK  (EXTENDED) CDB is formatted as shown in Table
       776, SEEK (EXTENDED) CDB.



                          Table 776
                     SEEK (EXTENDED) CDB


       The LBA  field specifies  the block address to seek to.
       When the  SEEK command completes without any errors the
       drive is positioned at the specified block address.


7.21.3    Error Conditions

       If  the   LBA  is  invalid,  the  drive  returns  CHECK
       CONDITION status.   The  sense data  is set  to ILLEGAL
       REQUEST/ILLEGAL BLOCK ADDRESS (05h/21h).

    XT-4000S Product Specification & OEM Technical Manual
SEND DIAGNOSTIC
    XT-4000S Product Specification & OEM Technical Manual
                                               SEND DIAGNOSTIC


7.22 SEND DIAGNOSTIC

       The SEND  DIAGNOSTIC  command  requests  the  drive  to
       perform diagnostic  tests.   This  command  is  usually
       followed by  the RECEIVE  DIAGNOSTIC  RESULTS  command,
       except when the self-test (SlfTst) bit is set to one.

       The SEND  DIAGNOSTIC  and  RECEIVE  DIAGNOSTIC  RESULTS
       commands support a number of vendor unique subcommands.
       See 7.22.4  Subcommands (SEND DIAGNOSTIC) later in this
       chapter, for details.


7.22.1    SCSI Deviations

       Except for  the  self-test,  the  specified  diagnostic
       command is  not executed  until the  drive  receives  a
       RECEIVE  DIAGNOSTIC   RESULTS  command  from  the  same
       initiator that issued the SEND DIAGNOSTIC command.

       The device off-line (DevOfl) and unit off-line (UntOfl)
       fields (see  Table 777,  SEND DIAGNOSTIC CDB) are only
       used for  the self-test  mode of  the  SEND  DIAGNOSTIC
       command.

       Except for  the self-test  mode, any  errors that occur
       during the  execution of  a diagnostic  subcommand  are
       reported as  a CHECK  CONDITION status  for the RECEIVE
       DIAGNOSTIC RESULTS  command.    This  condition  occurs
       because  the  diagnostic  subcommand  is  not  actually
       executed until  the RECEIVE  DIAGNOSTIC RESULTS command
       is issued.


7.22.2    Command Parameters

       The SEND DIAGNOSTICS CDB is formatted as shown in Table
       777, SEND DIAGNOSTIC CDB.




                          Table 777
                     SEND DIAGNOSTIC CDB


       The self-test (SlfTst) bit directs the drive to perform
       the self-test  on the  drive specified  in the CDB.  No
       device access occurs during this test.

    XT-4000S Product Specification & OEM Technical Manual
SEND DIAGNOSTIC

       The device  off-line (DevOfl)  bit is  not supported by
       the drive and is always set to zero.

       The unit  off-line (UntOfl)  bit directs  the drive  to
       perform the device diagnostics on the disk drive.  This
       bit is  only used when the self-test bit is set to one,
       and must be set to zero at all other times.

       The unit off-line (UntOfl) bit, in conjunction with the
       self-test bit,  specifies  the  type  of  tests  to  be
       performed by  the drive.   Table  778, SEND DIAGNOSTIC
       Drive  Self-Test   Options,  lists  and  describes  the
       options and the tests performed.




                          Table 778
           SEND DIAGNOSTIC Drive Self-Test Options


       The  device   diagnostics  perform   write  and  verify
       operations on  each surface  of the diagnostic cylinder
       of the specified drive.

       If any  sectors on  the diagnostic  cylinder cannot  be
       written  or   verified  by   using  two  different  bit
       patterns, the  drive returns  CHECK  CONDITION  status.
       The sense data is set to MEDIA ERROR/UNCORRECTABLE DATA
       ERROR (03h/11h).   The  sense information bytes contain
       the number of bad sectors found on this cylinder.

       The parameter  list length field, bytes three and four,
       specifies the  length (in  bytes) of the parameter list
       transferred from  the initiator to the drive during the
       DATA OUT  phase of  the SEND  DIAGNOSTIC command.   The
       parameter list contains a diagnostic subcommand and any
       additional information  required.   Each subcommand  is
       described in 7.22.4 Subcommands (SEND DIAGNOSTIC) later
       in this  chapter.   When the  self-test (SlfTst) bit is
       set to one, the parameter list length field must be set
       to zero.


7.22.3    Error Conditions

       If the  device off-line  (DevOfl) bit  is not zero, the
       drive returns  CHECK CONDITION status.   The sense data
       is  set   to  ILLEGAL   REQUEST/INVALID  FIELD  IN  CDB
       (05h/24h).

    XT-4000S Product Specification & OEM Technical Manual
                                               SEND DIAGNOSTIC

       If the self-test (SlfTst) bit is zero and the unit off-
       line (UntOfl)  bit is not zero, the drive returns CHECK
       CONDITION status.   The  sense data  is set to  ILLEGAL
       REQUEST/INVALID FIELD IN  CDB (05h/24h).

       If the  self-test (SlfTst)  bit is  set to  one and the
       parameter list  length field  is not  zero,  the  drive
       returns CHECK  CONDITION status.  The sense data is set
       to ILLEGAL REQUEST/INVALID FIELD IN CDB (05h/24h).

       If the diagnostic subcommand specified in the parameter
       list is  not legal,  the drive returns  CHECK CONDITION
       status.     The  sense   data  is   set  to     ILLEGAL
       REQUEST/INVALID FIELD IN PARAMETER LIST (05h/26h).


7.22.4    Subcommands


A    GET DRIVE STATUS SUBCOMMAND

       The GET  DRIVE STATUS  subcommand, shown in Table 779,
       GET DRIVE  STATUS Subcommand Parameter List, causes the
       drive to  return unmodified status from the drive.  The
       disk  drive   begins  to  execute  the  subcommand  and
       transfer the  status data  when  it  has  received  the
       appropriate RECEIVE DIAGNOSTIC RESULTS command from the
       initiator




                          Table 779
          GET DRIVE STATUS Subcommand Parameter List


       The subcommand  code field is set to 03h to specify the
       GET DRIVE STATUS diagnostic subcommand.

       The number  of bytes  to transfer  field specifies  the
       number of  status bytes  to transfer  to the  initiator
       during the RECEIVE DIAGNOSTIC RESULTS command.  The GET
       DRIVE STATUS  subcommand always  returns five bytes, or
       the number specified in this field, whichever is less.

       The remaining  bytes are  reserved and  must be  set to
       zero.

       Data for  the GET DRIVE STATUS diagnostic subcommand is
       transferred in  the format  shown in  Table  780,  GET
       DRIVE STATUS Data Format.

    XT-4000S Product Specification & OEM Technical Manual
SEND DIAGNOSTIC



                          Table 780
                 GET DRIVE STATUS Data Format


       The command  status field  indicates the  status of the
       command.   Table 781,  GET DRIVE STATUS Command Status
       Values, lists the possible values for this field.

       NOTE: If the  last ESDI  command to  the drive caused a
       fault condition,  the drive  returns the  status of the
       previous command.    Otherwise,  it  gets  the  current
       status from the drive.




                          Table 781
            GET DRIVE STATUS Command Status Values


       The ESDI drive status field indicates the status of the
       ESDI drive.   The  status returned  is specific  to the
       Maxtor  XT-4000E   Family  disk  drive.    For  further
       details,  see  XT-4000E  Product  Specification  &  OEM
       Manual.

       NOTE: The drive  clears the  ESDI  drive  status  field
       after it has processed the GET DRIVE STATUS subcommand.

       The vendor  unique status field specifies vendor unique
       status.


B    PASS DRIVE COMMAND SUBCOMMAND

       The PASS DRIVE COMMAND subcommand, shown in Table 782,
       PASS DRIVE  COMMAND Subcommand  Parameter List,  causes
       the drive  to pass the drive command from the initiator
       to the  disk drive.   The  drive begins  to execute the
       subcommand  and   transfer  status  data  when  it  has
       received the  appropriate  RECEIVE  DIAGNOSTIC  RESULTS
       command from the initiator.




                          Table 782
         PASS DRIVE COMMAND Subcommand Parameter List

    XT-4000S Product Specification & OEM Technical Manual
                                               SEND DIAGNOSTIC

       The subcommand  code is  set to 04h to specify the PASS
       DRIVE COMMAND diagnostic subcommand.

       The number  of bytes  to transfer  field specifies  the
       number of  status bytes  to transfer  to the  initiator
       during the  RECEIVE DIAGNOSTIC  RESULTS command.    The
       initiator may  request up  to 5  bytes of drive status.
       The PASS  DRIVE COMMAND  subcommand  always  returns  5
       bytes, or the number specified in this field, whichever
       is less.

       The drive command field specifies a command specific to
       the ESDI internal interface within the disk drive.  For
       further details,  see XT-4000E  Product Specification &
       OEM Manual.

       The remaining  bytes are  reserved and  must be  set to
       zero.

       The format  for the  status data returned from the PASS
       DRIVE COMMAND  diagnostic subcommand  is shown in Table
       783, PASS DRIVE COMMAND Status Data Format.



                          Table 783
            PASS DRIVE COMMAND Status Data Format


       The command  status field  indicates the  status of the
       command.  Table 784, PASS DRIVE COMMAND Command Status
       Values, lists the possible values for this field.




                          Table 784
           PASS DRIVE COMMAND Command Status Values


       The ESDI drive status field indicates the status of the
       ESDI disk  drive.   The status  returned is specific to
       the XT-4000E  and XT-8000E  Family disk  drives.    See
       Table 785, PASS DRIVE COMMAND Standard Status Response
       Bits.

       NOTE: The disk drive clears the ESDI drive status field
       after  it   has  processed   the  PASS   DRIVE  COMMAND
       subcommand.

    XT-4000S Product Specification & OEM Technical Manual
SEND DIAGNOSTIC



                          Table 785
       PASS DRIVE COMMAND Standard Status Response Bits



C    READ HEADER SUBCOMMAND

       The READ  HEADER diagnostic  subcommand, shown in Table
       786, READ HEADER Subcommand Parameter List, causes the
       drive to perform a read operation of the header address
       field for  all blocks  on a track.  The drive begins to
       execute the  subcommand and  transfer data  when it has
       received the  appropriate  RECEIVE  DIAGNOSTIC  RESULTS
       command from the initiator.




                          Table 786
            READ HEADER Subcommand Parameter List


       The subcommand  code is  set to 07h to specify the READ
       HEADER diagnostic subcommand.

       The block  address field specifies the block address on
       the track where the read header diagnostic operation is
       performed.

       The remaining byte is reserved and must be set to zero.

       The drive transfers data for the READ HEADER diagnostic
       subcommand during  the DATA  OUT phase,  in the  format
       shown in Table 787, READ HEADER Data Format.  The data
       format is repeated for each block in the track.




                          Table 787
                   READ HEADER Data Format





                          Table 788
             TRANSLATE Subcommand parameter List

    XT-4000S Product Specification & OEM Technical Manual
                                               SEND DIAGNOSTIC



                          Table 789
                    TRANSLATE Data Format


       The cylinder  number field indicate the cylinder number
       of the specified track.

       The head number field indicates the head number.

       The sector number field indicates the sector number.

       A defective  track (DT) bit of one indicates the entire
       track is defective.

       A spare  sector (SS)  bit of  one indicates  this is  a
       spare sector on the track

    XT-4000S Product Specification & OEM Technical Manual
START/STOP UNIT
    XT-4000S Product Specification & OEM Technical Manual
                                               START/STOP UNIT


7.23 START/STOP UNIT

       The START/STOP  UNIT command  requests that  the  drive
       spin up or spin down.


7.23.1    SCSI Deviations

       There are no deviations.


7.23.2    Command Parameters

       The CDB for the START/STOP UNIT command is formatted as
       shown in Table 790, START/STOP UNIT CDB.




                          Table 790
                     START/STOP UNIT CDB


       An immediate  (Immed) bit  of one indicates that status
       is  to   be  returned  as  soon  as  the  operation  is
       initiated.   If the  immediate bit  is zero,  the drive
       returns the status when the operation is completed.

       A start  bit of  one requests  that the  drive be  made
       ready for  use.   A start bit of zero requests that the
       drive be spun down.


7.23.3    Error Conditions

       If a  command which  accesses the  media is sent to the
       drive  after  a  STOP  UNIT  command  (START/STOP  UNIT
       command with  start  bit  equal  to  zero),  the  drive
       returns CHECK CONDITION status.   The sense data is set
       to NOT READY/DRIVE NOT READY (02h/04h).

    XT-4000S Product Specification & OEM Technical Manual
TEST UNIT READY
    XT-4000S Product Specification & OEM Technical Manual
                                               TEST UNIT READY


7.24 TEST UNIT READY

       The TEST  UNIT READY  command provides  a means for the
       initiator to check whether the drive is ready.


7.24.1    SCSI Deviations

       There are no deviations.


7.24.2    Command Parameters

       The CDB for the TEST UNIT READY command is formatted as
       shown in Table 791, TEST UNIT READY CDB.




                          Table 791
                     TEST UNIT READY CDB



7.24.3    Error Conditions

       If the  logical unit  is not ready, the drive returns a
       CHECK CONDITION  or BUSY  status in  response  to  this
       command.   A REQUEST  SENSE command  can be  issued  to
       obtain detailed  information about the reason the drive
       is not ready (unavailable).

    XT-4000S Product Specification & OEM Technical Manual
VERIFY
    XT-4000S Product Specification & OEM Technical Manual
                                                        VERIFY


7.25 VERIFY

       The VERIFY  command requests  that the drive verify the
       data  written  on  the  drive.    Verification  may  be
       performed either  as a  byte-by-byte comparison,  or by
       confirming that  the data  and ECCs  correspond to each
       other.


7.25.1    SCSI Deviations

       There are no deviations.


7.25.2    Command Parameters

       The VERIFY  CDB is  formatted as  shown in  Table 792,
       VERIFY CDB.




                          Table 792
                          VERIFY CDB


       A byte  check (BytChk)  bit of one causes the specified
       logical blocks  to be  read from  the disk and compared
       with the  data transferred from the initiator.  The ECC
       is  also   checked.    Data  is  transferred  from  the
       initiator in  a DATA  OUT phase,  just as  in  a  write
       operation.   If the  byte check  (BytChk) bit is set to
       zero, the  data is  read from  the disk  and the ECC is
       checked for  correctness;  no  DATA  OUT  phase  occurs
       between the initiator and the drive.

       The LBA  field specifies the logical block at which the
       verify operation begins.

       The verification  length field  specifies the number of
       contiguous logical  blocks of  data to  be verified.  A
       verification length  of zero  indicates that no data is
       verified and is not considered an error by the drive.


7.25.3    Error Conditions

       If the LBA is invalid, the drive terminates the command
       with CHECK  CONDITION status.  The sense data is set to
       ILLEGAL REQUEST/ILLEGAL BLOCK ADDRESS (05h/21h).

    XT-4000S Product Specification & OEM Technical Manual
                                                        VERIFY

       If the LBA, plus the verification length, results in an
       invalid block address, the drive terminates the command
       with CHECK  CONDITION status.  The sense data is set to
       ILLEGAL REQUEST/ILLEGAL BLOCK ADDRESS (05h/21h).

    XT-4000S Product Specification & OEM Technical Manual
WRITE
    XT-4000S Product Specification & OEM Technical Manual
                                                         WRITE


7.26 WRITE

       The WRITE  command requests  that the  drive write  the
       data transferred  by the  initiator to  the media.   It
       also causes the drive to perform an implied SEEK to the
       cylinder, head,  and sector  which corresponds  to  the
       specified LBA.


7.26.1    SCSI Deviations

       There are no deviations.


7.26.2    Command Parameters

       The CDB  for the WRITE command is formatted as shown in
       Table 793, WRITE CDB.




                          Table 793
                          WRITE CDB


       The LBA  field specifies the logical block at which the
       write operation begins.

       The transfer  length  field  specifies  the  number  of
       contiguous logical blocks of data to be transferred.  A
       transfer length  of zero  indicates  that  256  logical
       blocks are transferred.


7.26.3    Error Conditions

       If the  LBA is  invalid or if the LBA plus the transfer
       length result  in an  invalid block  address, the  disk
       drive  terminates  the  command  with  CHECK  CONDITION
       status.     The  sense   data   is   set   to   ILLEGAL
       REQUEST/ILLEGAL BLOCK  ADDRESS (05h/21h).   No  data is
       transferred if this condition occurs.

    XT-4000S Product Specification & OEM Technical Manual
WRITE (EXTENDED)
    XT-4000S Product Specification & OEM Technical Manual
                                              WRITE (EXTENDED)


7.27 WRITE (EXTENDED)

       The WRITE  (EXTENDED) command  requests that  the drive
       write the  data transferred  by the  initiator  to  the
       media.   It also causes the drive to perform an implied
       SEEK  to   the  cylinder,   head,  and   sector   which
       corresponds to the specified LBA.


7.27.1    SCSI Deviations

       There are no deviations.


7.27.2    Command Parameters

       The CDB  for the  WRITE (EXTENDED) command is formatted
       as shown in Table 794, WRITE (EXTENDED) CDB.



                          Table 794
                     WRITE (EXTENDED) CDB


       The LBA  field specifies the logical block at which the
       write operation begins.

       The transfer  length  field  specifies  the  number  of
       contiguous logical  blocks of data to be transferred. A
       transfer length  of zero  indicates  that  no  data  is
       transferred, and  is not  considered an  error  by  the
       drive.


7.27.3    Error Conditions

       If the LBA field is invalid, and/or if the LBA plus the
       transfer length result in an invalid block address, the
       drive  terminates  the  command  with  CHECK  CONDITION
       status.     The  sense   data   is   set   to   ILLEGAL
       REQUEST/ILLEGAL BLOCK  ADDRESS (05h/21h).   No  data is
       transferred if this condition occurs.

    XT-4000S Product Specification & OEM Technical Manual
WRITE & VERIFY
    XT-4000S Product Specification & OEM Technical Manual
                                                WRITE & VERIFY


7.28 WRITE AND VERIFY

       The WRITE  AND VERIFY  command requests  that the drive
       write the  data transferred  from the  initiator to the
       disk drive  and then  verify that the data is correctly
       written.     The  drive   supports   both   the   media
       verification against  ECC, and  byte-by-byte comparison
       options.


7.28.1    SCSI Deviations

       There are no deviations.


7.28.2    Command Parameters

       The WRITE AND VERIFY CDB is formatted as in Table 795,
       WRITE AND VERIFY CDB.




                          Table 795
                     WRITE AND VERIFY CDB


       A byte  check (BytChk)  bit of one causes the specified
       logical blocks  to be  read from  the disk and compared
       with the  data transferred from the initiator.  The ECC
       is  also   checked.    Data  is  transferred  from  the
       initiator in  a DATA  OUT phase,  just as  in  a  write
       operation.   If the  byte check  (BytChk) bit is set to
       zero, the  data is  read from  the disk  and the ECC is
       checked for  correctness;  no  DATA  OUT  phase  occurs
       between the initiator and the disk drive.
       The LBA  field specifies the logical block at which the
       write operation begins.

       The transfer  length  field  specifies  the  number  of
       contiguous logical  blocks of  data are transferred.  A
       transfer length  of  zero  indicates  that  no  logical
       blocks  are   transferred.     This  condition  is  not
       considered an  error and no data is written.  Any other
       value indicates  the number  of logical blocks that are
       transferred.

    XT-4000S Product Specification & OEM Technical Manual
WRITE BUFFER
    XT-4000S Product Specification & OEM Technical Manual
                                                  WRITE BUFFER


7.29 WRITE BUFFER

       The WRITE  BUFFER command  is used  in conjunction with
       the READ  BUFFER command,  as a diagnostic function for
       testing the  disk drive's  data buffer  memory and  the
       SCSI bus  integrity. There is no media access with this
       command.

       To determine  the maximum  amount of  data that  can be
       transferred with  the  READ  BUFFER  and  WRITE  BUFFER
       commands, the initiator can issue a READ BUFFER command
       with the  allocation length  field set  to four.  Bytes
       two and three contain the maximum buffer size.


7.29.1    SCSI Deviations

       There are no deviations.


7.29.2    Command Parameters

       The WRITE  BUFFER CDB  is formatted  as shown  in Table
       796, WRITE BUFFER CDB.




                          Table 796
                       WRITE BUFFER CDB


       This command does not alter the medium of the drive.

       The function  of this command and the meaning of fields
       within the  command  descriptor  block  depend  on  the
       contents of  the mode  field.   The drive supports only
       the combined header and data mode (000b).


7.29.3    Data Format

       The combined  header and  data mode  specifies that the
       data to  be transferred  is  preceded  by  a  four-byte
       header.   The four-byte header consists of all reserved
       bytes.  The buffer ID and the buffer offset fields must
       be zero.  The parameter list length field specifies the
       maximum number of bytes that are transferred during the
       DATA OUT  phase.   This number  includes four  bytes of
       header, so the data length to be stored in the target's

    XT-4000S Product Specification & OEM Technical Manual
WRITE BUFFER

       buffer is  parameter  list  length  minus  four.    The
       initiator should  attempt to  ensure that the parameter
       list length is not greater than four plus the available
       length that  is returned  in the  header  of  the  READ
       BUFFER command  (mode 00b).    If  the  parameter  list
       length exceeds  the available  length  plus  four,  the
       drive returns  CHECK CONDITION  status.  The sense data
       is set to ILLEGAL REQUEST.




                          Table 797
                Combined Header and Data Mode



7.29.4    Error Conditions

       If the  byte transfer  length exceeds  the size  of the
       drive's buffers,  the  command  terminates  with  CHECK
       CONDITION status.   The  sense data  is set  to ILLEGAL
       REQUEST/ILLEGAL FIELD IN CDB (05h/24h).

    XT-4000S Product Specification & OEM Technical Manual
WRITE LONG
    XT-4000S Product Specification & OEM Technical Manual
                                                    WRITE LONG


7.30 WRITE LONG

       The WRITE  LONG command requests the drive to perform a
       write operation  of one data block and the six bytes of
       ECC information. The data and the six ECC bytes for the
       specified logical  block are  supplied by the initiator
       during the DATA OUT phase.


7.30.1    SCSI Deviations

       The drive  recognizes either  EAh or  3Fh as  being the
       WRITE LONG  command.  Maxtor implemented EAh before the
       SCSI-2 definition  of 3Fh.   The  EAh form  is a vendor
       unique  command,  and  thus  is  outside  of  the  SCSI
       standard.   The 3Fh  form of the command is the defined
       SCSI-2 version of the WRITE LONG command.

       The Maxtor  vendor unique  definition differs  from the
       SCSI-2 definition  in that  Maxtor (EAh)  defines bytes
       seven and  eight of  the CDB  as always  equal to zero,
       and the  transfer length is always one sector (plus the
       ECC bytes).


7.30.2    Command Parameters

       The CDB  for the  WRITE LONG  command is  formatted  as
       shown in Table 798, WRITE LONG CDB.



                          Table 798
                        WRITE LONG CDB


       The block  address field  specifies the  block at which
       the write long operation begins.

       CAUTION:     The physical location of the READ LONG and
       WRITE LONG block address is computed using the physical
       sector size instead of the logical block size.


7.30.3    Error Conditions

       If the LBA is invalid, the drive terminates the command
       with CHECK  CONDITION status.  The sense data is set to
       ILLEGAL REQUEST/ILLEGAL BLOCK ADDRESS (05h/21h).

    XT-4000S Product Specification & OEM Technical Manual
WRITE LONG  (SCSI-2)
    XT-4000S Product Specification & OEM Technical Manual
                                          WRITE LONG  (SCSI-2)


7.31 WRITE LONG (SCSI-2)

       The WRITE  LONG command  requests that  the drive write
       the data  transferred by  the initiator  to the medium.
       The data  passed  during  the  WRITE  LONG  command  is
       includes the  data bytes  and the ECC bytes.  See Table
       799, WRITE LONG Command.




                          Table 799
                      WRITE LONG Command


       The logical  block address  field specifies the logical
       block at which the data is written.

       The byte  transfer length field specifies the number of
       bytes of  data that the drive returns for the READ LONG
       command.   If a  non-zero byte transfer length does not
       exactly match the data length the drive returns for the
       READ  LONG  command,  then  the  drive  terminates  the
       command with CHECK CONDITION status.  The sense data is
       set to  ILLEGAL REQUEST/INVALID  FIELD IN  CDB. The ILI
       and valid bits are set to one and the Information field
       is set  to the difference of the requested length minus
       the actual  length  in  bytes.    Negative  values  are
       indicated by  two's complement  notation.   A  transfer
       length of  zero indicates that no bytes are transferred
       and is not considered an error.

    XT-4000S Product Specification & OEM Technical Manual
    XT-4000S Product Specification & OEM Technical Manual

























































Doc 1014995, Rev B           1            Maxtor Corporation
Doc 1014995, Rev B           1            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


APPENDIX A:  DISCONNECT/RECONNECT CONDITIONS

       This section  describes the  conditions under which the
       drive disconnects from, and reconnects to the SCSI bus.
       These are  the default  options provided  by the drive,
       but may  be modified  by the  initiator using  the MODE
       SELECT command.
       The normal  DISCONNECT/RECONNECT options stress maximum
       throughput,  yet   do  not  monopolize  the  SCSI  bus,
       providing maximum bus use.  These options would be used
       in  a   multiple  initiator  environment.    Also,  the
       initiator should  be capable  of sustaining  a SCSI bus
       throughput which  is equal  to, or  greater  than,  the
       drive's internal data transfer rate.

       To disable  disconnects, the  initiator should  not set
       bit six in the ID message that it sends at the start of
       a command.   If the drive is processing a command which
       does not support disconnects (bit six in the ID message
       equals zero),  and any  other command  is  active,  the
       drive immediately  terminates the  command that  cannot
       disconnect with  a  BUSY  status.    If  normal  system
       operation includes  multiple commands sent to the drive
       simultaneously,  the   initiator  should   enable   the
       DISCONNECT/RECONNECT option  (bit six in the ID message
       set to one).

       The disconnect/reconnect conditions are as follows:

         When the SCSI bus is anticipated to be idle (no -REQ
          is active)  for the  amount of time specified in the
          MODE SELECT  command bus inactivity limit field, the
          drive automatically disconnects from the SCSI bus.

         When a drive receives a command while a command from
          another initiator  is active,  the drive disconnects
          from the  bus as soon as the entire command from the
          initiator has been received.

         READ commands  always disconnect  immediately  after
          receipt of  the command.   This allows access to the
          SCSI bus during the disk latency and/or seek time.

         When  executing   a  READ   command,  if  the  drive
          anticipates that  the bus  will be  idle for  longer
          than the  time specified  in  the  MODE  SELECT  bus
          inactivity limit  field, the  drive disconnects from
          the bus  as soon as the bus becomes idle.  The drive
          then  reconnects   when  data  is  available  to  be
          transferred.   This condition  may occur if:  1) the
          read operation  crosses a  cylinder boundary  and  a





Doc 1014995, Rev B           2            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


          seek operation  is required;  2) a seek operation to
          an alternate  track is required; or 3) the SCSI data
          transfer rate  is greater  than the drive's internal
          data transfer rate and the buffer has been emptied.

         When the  drive receives  a WRITE  command, it reads
          data from the initiator until the internal buffer is
          filled.   Once the buffer is filled, or all the data
          has been transferred, the drive disconnects from the
          bus.   The reconnect occurs when the drive starts to
          write data  to the  disk, and  the  internal  buffer
          becomes available  for more  data to  be transferred
          from the  initiator.  A reconnect also occurs, after
          all the data has been written to the disk, to return
          the status and terminate the command.










































Doc 1014995, Rev B           3            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
    XT-4000S Product Specification & OEM Technical Manual

























































Doc 1014995, Rev B           5            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


APPENDIX B:  DEFECT MANAGEMENT

       There are  four different  ways in which defects can be
       managed in the XT-4000S Family disk drives:

         Cylinder-Oriented.   Each cylinder  is  an  integral
          unit, with  the alternates per zone number of spares
          assigned to  the cylinder.  A defect anywhere within
          the cylinder  is reassigned  by invoking  one of the
          spare sectors,  which are  initially located  at the
          end of  the last  track of  the cylinder.    If  the
          number of  reassigned sectors  exceeds the number of
          spare  sectors,   one  track   of  the  cylinder  is
          relocated to  the area  of the  drive defined by the
          alternate tracks per volume field.

         Track-Oriented.   Each track  is an  integral  unit,
          with one  or more  spares assigned  to the track.  A
          defect anywhere  within the  track is  reassigned by
          invoking  one   of  the  spare  sectors,  which  are
          initially located  at the  end of  the  track,  just
          prior to index.  If the number of reassigned sectors
          exceeds the  number of  spare sectors,  the track is
          relocated to  the area  of the  drive defined by the
          alternate tracks per volume field.

         Drive-Oriented.   The entire  drive is  an  integral
          unit, with  the alternates per zone number of spares
          assigned to  the drive.   A  defect anywhere  on the
          drive is  reassigned by relocating the sector to one
          of the  spare sectors, which are located in the area
          of the  drive defined  by the  alternate tracks  per
          volume field.

         Host Defect  Management.   The entire  drive  is  an
          integral unit, with no spares.  A defect anywhere on
          the drive  is  deallocated  by  the  host  operating
          system,  and   future  access  to  this  sector  are
          inhibited.   An error occurs if you use the REASSIGN
          BLOCK command in this mode.

       Set  the   MODE  SELECT  values  of  tracks  per  zone,
       alternate sectors  per zone,  and alternate  tracks per
       volume,  as  shown  in  Table  B1,  Defect  Management
       Selections, to choose one of the four techniques.




                          Table B1
                 Defect Management Selections

    XT-4000S Product Specification & OEM Technical Manual


       NOTE: The alternate  sectors per  zone,  and  alternate
       tracks per  volume, field  values  are  recommended  by
       Maxtor for most applications, but may vary per customer
       requirements  of  capacity  versus  performance.    For
       example, if  cylinder-oriented mode  is  selected,  the
       systems integrator  may elect  to increase  capacity by
       reserving fewer  alternate  sectors  per  zone.    This
       increases the  probability that  a track may have to be
       relocated because  of more  defects than  spares  in  a
       given cylinder,  so the  number of alternate tracks per
       volume may need to be increased.  Also, performance may
       be degraded as a result of the additional SEEKs imposed
       by track relocation.


REASSIGNMENT SEQUENCES

       When  a   defective  area   is  found,  a  reassignment
       algorithm is  invoked by  either the  REASSIGN BLOCK or
       FORMAT  UNIT   command,  and  multiple  blocks  may  be
       reassigned in  one  operation.    For  simplicity,  the
       following reassignment  sequences assume a single block
       reassignment.


Cylinder-Oriented Reassignment Sequence

       1. The designated  block is  located,  and  the  entire
          cylinder in  which it  resides is verified to ensure
          that there are no unflagged defects.
       2. The cylinder  is copied  to  the  reserved  cylinder
       (MAX-1).

       3. Flags in  the configuration area (cylinder zero) are
          updated, to  indicate completion  of the first phase
          in case  a power  failure or  RESET  interrupts  the
          process.

       4. The  affected  cylinder  is  reformatted,  with  the
          headers updated  to "slip"  the bad  block  and  all
          following blocks  (up to the end of the cylinder) by
          one.   This causes  some logical blocks to move from
          the last position on one track to the first position
          on the  next track,  but all  blocks are  contiguous
          within the cylinder.

       5. Flags in  the  configuration  area  are  updated  to
          indicate completion of the second phase.

       6. The content  of the reserved cylinder is copied back
       to the original cylinder.





Doc 1014995, Rev B           7            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       7. Flags in  the  configuration  area  are  updated  to
       indicate completion of the operation.

       In the  event that there are insufficient spares in the
       cylinder,  one  of  the  tracks  in  the  cylinder  are
       relocated to  the area  defined by the alternate tracks
       per volume.   These are located in the area ending with
       cylinder MAX-2  (the starting  cylinder depends  on the
       number of  alternate tracks, which is always a multiple
       of the number of heads).  This restores to the cylinder
       those spares  which had been consumed by the defects in
       this track,   and reduces the probability that a future
       reassignment in  the same  cylinder results  in a track
       relocation.

       When a  SEEK is  performed to  an LBA  which  has  been
       reassigned, the following sequence applies:

       1. The drive  SEEKs to  the cylinder and head where the
          sector was  originally located,  and begins a search
          for the header.

       2. Upon reading the first header encountered, the drive
          determines whether  the target  sector is within the
          current track.   Information in the header indicates
          the number  of the last sector on the current track,
          and whether the track has been relocated.

       3. If the  target sector  was once  the last  one on  a
          track, and has been rolled over to the next track in
          the cylinder due to a reassignment, this is detected
          from the  "last sector"  information in  the  header
          that was  read,  and  a  head  switch  is  performed
          immediately.
       4. If the  track has been relocated, the drive SEEKs to
          the alternate  area.   If the  data transfer is long
          enough to  go beyond  the end  of the  track, a SEEK
          back  to   the  original  cylinder  takes  place  to
          continue the transfer.


Track-Oriented Reassignment Sequence

       1. The designated  block is  located,  and  the  entire
         track in which it resides is verified, to ensure that
         there are no unflagged defects.

       2. The track  is copied  to a  track  in  the  reserved
       cylinder (MAX-1).

    XT-4000S Product Specification & OEM Technical Manual


       3. Flags in  the configuration area (cylinder zero) are
         updated, to indicate completion of the first phase in
         case a power failure or RESET interrupts the process.

       4. The affected  track is reformatted, with the headers
         updated to  "slip" the  bad block  and all  following
         blocks (up  to the  end of  the track)  by one.   All
         blocks are contiguous within the track.

       5. Flags in  the  configuration  area  are  updated  to
         indicate completion of the second phase.

       6. The content  of the  reserved area is copied back to
       the original track.

       7. Flags in  the  configuration  area  are  updated  to
       indicate completion of the operation.

       In the  event that there are insufficient spares in the
       track, the  entire  track  is  relocated  to  the  area
       defined by the alternate tracks per volume field.

       When a  SEEK is  performed to  an LBA  which  has  been
       reassigned, the following sequence applies:

       1. The drive  SEEKs to  the cylinder and head where the
         sector was  originally located,  and begins  a search
         for the header.

       2. Upon reading the first header encountered, the drive
         determines whether the track has been relocated.

       3. If the  track has been relocated, the drive SEEKs to
         the alternate  area.   If the  data  transfer  length
         extends beyond the end of the relocated track, a SEEK
         back to the original cylinder takes place to continue
         the transfer.


Drive-Oriented Reassignment Sequence

       1. The designated  block is  copied to  a sector in the
       reserved cylinder (MAX-1).

       2. The header of the designated block is written with a
          pattern which indicates that it has been relocated.
       In the  event that there are insufficient spares in the
       reserved area,  the drive  returns an  error  condition
       indicating that no spares are available.







Doc 1014995, Rev B           9            Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual


       When a  SEEK is  performed to  an LBA  which  has  been
       reassigned, the following sequence applies:

       1. The drive  SEEKs to  the cylinder and head where the
          sector was  originally located,  and begins a search
          for the header.

       2. Upon reading the target header, the drive determines
          that the sector has been relocated.

       3. The drive  SEEKs to the alternate area to access the
          requested LBA.  A SEEK back to the original cylinder
          takes place to continue the transfer, if necessary.


Host Defect Management Sequence

       1. The defective  block is  allocated to either a dummy
       file or a "bad block" list.

       2. The host  ensures that  no accesses are performed to
       the defective block.


DEFECT MANAGEMENT ASSUMPTIONS AND STATISTICS

       In order  to choose a defect management mode, it may be
       useful  to   examine  some   of  the   assumptions  and
       statistics which affect the media.

       The number  of spares allocated must make allowance for
       the sum of:

         the initial  maximum number  of defects specified by
          the manufacturer  (less than  or equal  to  one  per
          unformatted megabyte)

         any additional defects found at receiving inspection
       and system integration

         the  additional  "grown"  defects  which  accumulate
       during the life of the drive

       The  following   tables,  Table   B2  and  Table  B3,
       illustrate  the   effect  of   spares  and  defects  on
       capacity.




                          Table B2
               Spares Versus Capacity, XT-4380

    XT-4000S Product Specification & OEM Technical Manual




                          Table B3
               Spares Versus Capacity, XT-4170





















































Doc 1014995, Rev B           11           Maxtor Corporation

    XT-4000S Product Specification & OEM Technical Manual
    XT-4000S Product Specification & OEM Technical Manual



    XT-4000S Product Specification & OEM Technical Manual


APPENDIX C:  CDB BIT DEFINITIONS

          Abbreviation   Meaning


          ARRE automatic read reallocation enabled bit
          AWRE automatic write reallocation enabled bit
          BytChk    byte check bit
          DCR  disable correction bit
          DCRT disable certification bit
          DevOfl    device off-line bit
          DPRY disable primary bit
          DT   defective track bit
          DTE  disable transfer on error bit
          EEC  enable early correction bit
          FmtData   format data bit
          FOV  format options valid bit
          HSEC hard sector format bit
          ILI  incorrect length indicator bit
          Immed     immediate bit
          INS  inhibit save bit
          PCF  page control field bit
          PER  post error bit
          PF   page format bit
          PMI  partial medium indicator bit
          PS   parameters saveable bit
          RC   read continuous bit
          RelAdr    relative address bit
          RMB  removable media bit
          SlfTst    self-test bit
          SP   save parameters bit
          SS   spare sector bit
          SSEC soft sector format bit
          STPF stop format bit
          SURF surface bit
          TB   transfer block bit
          3rdPty    third party reservation bit
          UntOfl    unit off-line bit
          VU   vendor unique bit
          WP   write protect bit

    XT-4000S Product Specification & OEM Technical Manual
    XT-4000S Product Specification & OEM Technical Manual



    XT-4000S Product Specification & OEM Technical Manual


APPENDIX D:  UNITS OF MEASURE

          Abbreviation   Meaning


          A/m  amps per meter
          AWG  American wire gauge
          bpi  bits per inch
          dBa  decibel, A-weighted
          fci  flux changes per inch
          g    gram
          Gbyte     gigabyte
          Hz   hertz
          mA   milliamp
          A   microamp
          Mbit megabit
          Mbyte     megabyte
          m   micrometer
          msec millisecond
          sec microsecond
          nsec nanosecond
          Oe   oersted
          RH   relative humidity
          rpm  revolutions per minute
          tpi  tracks per inch
          xxb  binary values
          xxh  hexadecimal values


APPENDIX E:  BUFFER RATIO APPLICATIONS

WHAT ARE THE BUFFER RATIOS?

       The Buffer Ratios indicate to the target how full, on a
       READ command,  or how  empty, on  a WRITE  command, the
       buffer should be prior to attempting reselection.

       SCSI MODE  SELECT parameter  page 2  defines the Buffer
       Ratio  parameters   as  numerators   of  a   fractional
       multiplier that  has 256  (FFh) as  its denominator.  A
       value of  128 (80h) would equate to a ratio of 50%, and
       192 (C0h)  equates to a ratio of 75%, etc.  In standard
       SCSI, the  percentage is  applied to  the total size of
       the data  buffer.   In Maxtor's  implementation of  the
       Buffer Ratios,  the percentage is applied to either the
       data buffer  or the  data transfer,  whichever is less.
       In other  words, if  the data transfer is less than the
       disk buffer,  the Buffer  Ratio will  be applied to the
       transfer length.   If the data transfer is greater than
       the disk  buffer, the  Buffer Ratio  will be applied to
       the disk  buffer.  This implementation allows one value
       be used  for the  Buffer Ratios, regardless of the data
       transfer length.


WHAT ARE THE PERFORMANCE BENEFITS FROM BUFFER RATIOS?

       The performance  benefit from the Buffer Ratios is in a
       multi-target environment  where SCSI  "on-bus" time  is
       critical.   The Buffer  Ratios ensure  that the time on
       the SCSI  bus is  minimized and  the data transfer rate
       across the SCSI bus is maximized.


BUFFER FULL RATIO

       Without  the   Buffer  Full   Ratio  the  target  would
       reconnect to  the SCSI  bus as  soon as  data is in the
       buffer.   If the  SCSI bus transfer rate is higher then
       the disk  transfer rate,  the  transfer rate across the
       SCSI bus  will slow  to that  of the  disk.   This will
       increase the  total time  on the  bus for  a given data
       transfer.   Figure E1.  shows this condition where the
       "Hold-off Time"  is minimal and the "Total Time on Bus"
       is significant.   Note  that if  the SCSI  bus transfer
       rate is  lower than  the disk transfer rate, the Buffer
       Full Ratio  should  be  zero  (disabled).    This  will
       optimize performance  in  slower  systems  and  is  the
       default value for the Buffer Ratios.

                          Figure E1
         Data Transfer Rate Without Buffer Full Ratio


       With Buffer  Full Ratio,  the target  will  "Hold  off"
       reconnecting to the bus until the desired percentage of
       data is  in the  buffer to ensure that the maximum SCSI
       bus rate  can be achieved.  This maximizes the SCSI bus
       rate and  minimizes total  "On-Bus" time.   Figure E2.
       shows that  by increasing  the "Hold-off Time" the SCSI
       bus transfer  rate is  maximized and the "Total Time on
       Bus" is  minimized,  with  the  "Total  Time  to  Data"
       remaining the  same.    Minimizing  the total  "On bus"
       time is  essential for  performance in  a  multi-target
       environment.




                          Figure E2
          Data Transfer Rate With Buffer Full Ratio



BUFFER EMPTY RATIO

       The Buffer  Empty Ratio  applies to  how empty of Write
       Data the buffer should be before reconnecting to obtain
       more Write  Data.   Maxtor's SCSI  implementation "pre-
       reads" Write  Data into  the data buffer directly after
       the WRITE  command is decoded.  Because the size of the
       data buffer is 45,056 bytes the Buffer Empty Ratio will
       only apply  to WRITE  commands with data transfers over
       45,056 bytes  per command and a disconnect/reconnect is
       required for  the remaining  data.   If WRITE  commands
       have long  data transfers,  it is  recommended that the
       Buffer Full Ratio and the Buffer Empty Ratio be Equal.


WHAT VALUE SHOULD BE USED FOR THE BUFFER RATIOS?

       The value  chosen  for  the  Buffer  Ratios  should  be
       selected to  optimize the  difference between  the disk
       speed and  the SCSI bus speed.  In Figures E1 and E2,
       the difference  in speed between the disk data rate and
       the SCSI  bus are  reflected by a difference in slopes,
       with a steep slope representing a higher speed.

       Table E1  below shows  the calculated  values for  the
       Buffer Ratios with the given SCSI bus speed.

                          Table E1
                     Buffer Ratio Values


APPENDIX F:  THE READ-AHEAD FEATURE

WHAT IS READ-AHEAD?

       Read-Ahead is a form of data caching where data is read
       from the  disk to  the buffer in anticipation of future
       operations.   This feature  can greatly  improve system
       access times  and throughput  in many  applications  by
       reducing the  time required  to make  data available to
       the host.   Read-Ahead  can be  switched on  or off  by
       means of the MODE SELECT command.


HOW DOES IT WORK?

       To understand  how Read-Ahead works, it is first useful
       to examine  how  data  is  stored  in  typical  systems
       applications.

       The tracks  on a  drive are divided into sectors as the
       smallest addressable  unit of  storage.  Data is stored
       as files  of various  lengths, with  one  sector  as  a
       minimum, but  most files  are spread across a number of
       sectors.  When a file spans multiple sectors, it can be
       stored and  retrieved most  quickly if  the sectors are
       written consecutively,  and so  most operating  systems
       allocate a  contiguous group  of sectors to a file, and
       write the  data in  a sequential  fashion  within  this
       allocated area.   Thus, although the drive is a random-
       access device,  files tend to be localized, and much of
       the data  transferred is  sequential.   As applications
       use larger  files (such  as the  multimegabyte graphics
       images created by CAD workstations), disk accesses tend
       to become more sequential.

       When retrieving  a file stored in this way, the highest
       performance is  achieved if  a single  READ command  is
       issued, with  the transfer length field set to the full
       length of  the file.   In  reality,  however,  this  is
       rarely the  case.   In operating  systems such as UNIX,
       READ commands  are usually issued with a fixed transfer
       length  (typically  1  to  8  kilobytes),  and  several
       successive commands  are required  to  retrieve  larger
       files.

       When an  access of  many  sectors  is  broken  up  into
       smaller commands,  it is  not possible  to transfer the
       data in  the most efficient way, because the time delay
       between the completion of one command and the beginning
       of the  next is  much longer  than the gap time between
       adjacent sectors.   By  the time  the next  command has
       been received,  the disks  have already  rotated beyond       the start  of
the  next consecutive  sector, so  it  is
       usually necessary  to wait  for nearly  a full  latency
       period before  the disk  drive is  able to continue the
       data transfer.    Obviously,  this  additional  latency
       increases the  time required  to read  the entire file,
       and significantly degrades performance.

       As an  example, consider  the situation shown in Figure
       F1, Sequential READs without Read-Ahead.

       1. The host  issues a  command to read sectors zero and
       one.

       2. Some amount  of latency is required to arrive at the
       starting sector.

       3. Data is read from the disk to the data buffer.

       4. When one full sector is available in the buffer, the
          drive starts to transfer data to the host.

       5. After all  the data  has been  sent to  the host and
          status  information  has  been  provided,  the  host
          prepares to send the next command.

       6. The second command (requesting a READ of sectors two
          and three) arrives, well after the heads have passed
          the start  of sector  two.  almost a full revolution
          is required before sector two rotates back around to
          the read/write head.




                          Figure F1
             Sequential READs without Read-Ahead


       Read-Ahead avoids  the loss  of performance represented
       by step  five by  taking advantage  of the disk drive's
       idle time  to read  additional data  into  the  buffer.
       There it  is available  for immediate  transfer in  the
       event that  the next READ command requests blocks which
       are already  in the buffer.  The probability of a "hit"
       (a match between data requested and data in the buffer)
       is  relatively   high  in   systems  which  store  data
       contiguously.

       When the  initiator sends  a READ command to the drive,
       it appears  to complete  normally.   In the background,
       however, while  the  system  is  obtaining  status  and       preparing to
send the  next command,  the  disk  drive
       continues to read data from the disk to the buffer.  If
       the next  command is also a READ, the disk drive checks
       to see  if the  requested data is in the buffer, and if
       so, the  data is  transferred to  the host immediately,
       without a delay for rotational latency.

       Of course,  not all  READ commands  request  contiguous
       sectors, so it is important that the Read-Ahead feature
       not impair  performance when  it is  not needed.    For
       example, if  the disk  drive is  reading ahead  and the
       next command  received is  anything other  than a  READ
       command (e.g. WRITE, SEEK, etc.), or the new command is
       a READ command for logical blocks which are not already
       in the  buffer, the  Read-Ahead  operation  immediately
       aborts and the new command is executed.

       Additionally, the  host system  can disable  Read-Ahead
       via the  MODE SELECT  command if  it is known that data
       accesses will be largely random rather than sequential.
       This technique  avoids the  overhead (approximately 100
       microseconds) associated  with checking  the buffer  to
       see if requested data is already present.


KEY READ-AHEAD PARAMETERS

       Size of  Read-Ahead Buffer:   The Read-Ahead buffer has
       45 kilobytes.   This is equivalent to approximately one
       and a half tracks.

       When Invoked:   If enabled, Read-Ahead is automatically
       performed after every READ or READ (EXTENDED) command.

       When Aborted:   Read-Ahead  is aborted  for any  of the
       following reasons.
         The buffer  has been  filled with  45  kilobytes  of
       data.

         A new  command is  received  which  is  not  a  READ
          command, or  which requires an access to a different
          area of the disk.

         A data error occurs while reading ahead.

         A SEEK  is required  to continue  reading ahead (for
         example, a cylinder boundary is encountered) with the
         RAMD bit set to zero in page code 38h.
CONTROLLING THE READ-AHEAD FEATURE
       The Read-Ahead  feature is controlled by either setting
       the read cache disable bit (RCD) to zero in the caching
       page (page code 08h) or by setting the cache enable bit
       (CE) to  one in  the read-ahead control page (page code
       38h).  See Table 729 or Table 743.


READ ALGORITHM

       The sequence  of a READ command varies depending on the
       answers to  the following questions:  (a) is Read-Ahead
       enabled, (b)  is the READ command requesting data which
       has been  prefetched, and  (c) does the transfer length
       exceed the  range of  data which  has been  prefetched,
       thus requiring  a media  access.   See Table  F1, READ
       Algorithm.




                          Table F1
                        READ Algorithm



READ-AHEAD PERFORMANCE

       The performance  benefits of  Read-Ahead vary depending
       on the  operating system and application programs.  The
       greatest benefits  will be  seen in  UNIX-based systems
       which transfer  large blocks  of data  with few  users,
       such as  graphics workstations.  The least benefit will
       be seen  in systems  with many  users and  short files,
       such  as  transaction  processing.    The  greater  the
       randomness of disk accesses, the less likely it is that
       the next  command  will  request  data  that  has  been
       prefetched.


GLOSSARY
       ack.  Acknowledge

       adr.  Address

       ANSC.  American National Standards Committee

       ANSI.  American National Standards Institute

       arbitration winner.   The arbitrating SCSI device which
          has the highest SCSI address.

       assert.  A signal driven to the true state.
       async.  Asynchronous

       BCV.  Buffer control valid

       bit.  Binary digit

       byte.  Eight consecutive binary digits

       C/C.  Continuous/composite (format)

       C/D.  CONTROL/DATA signal

       CCS.  Common Command Set

       CDB.   Command descriptor  block, the structure used to
          communicate requests from an initiator to a drive.

       cmd.  Command

       connect.   The function  that occurs  when an initiator
          selects a target to start an operation.

       CRC.  Cyclic redundancy check

       CSA.  Canadian Standards Association

       DB (7-0, P).  Eight data-bit signals, plus a parity-bit
       signal, that form a data bus.

       DC.  Direct current

       DCR.  Disabled correction (signal)

       disconnect.   The function  that occurs  when a  target
          releases control  of the  SCSI bus allowing it to go
          to the BUS FREE phase.
       DMA.  Direct memory access
       EBP.  Erase bypass

       ECC.  Error correction code

       ECL.  Emitter-coupled logic

       EDAC.  Error detection and correction

       EIA.  Electrical Industry Association

       ENDEC.  Encoder/decoder

       EPROM.  Erasable programmable read-only memory

       ERA.  Erase all

       FIFO.    First-in,  first-out,  storage  and  retrieval
       technique

       FCC.  Federal Communication Commission

       firmware.  Computer programs encoded permanently into a
       ROM

       FW.  Firmware

       G.  Constant of gravitation

       gnd.  Ground

       hard  error.     An  error  due  to  faulty  equipment,
          transmission techniques, recording media, etc.

       HDA.  Head disk assembly

       hex.  Hexadecimal

       HW.  Hardware

       I/O.  Input and/or output

       initiator.   A SCSI device, usually a host system, that
          requests that  an operation  be performed by another
          SCSI device.

       INTERMEDIATE status.   A status code sent from a target
          to an initiator upon completion of each command in a
          set of  linked commands, except for the last command
          in the set.
       ISG.  Inter-sector gap
       ISO.  International Standardization Organization

       LBA.  Logical block address

       LED.  Light-emitting diode

       logical thread.   The logical path which exists between
          an initiator's  memory and  a bus  device LUN,  even
          though the physical path may be disconnected.

       logical unit.  A physical or virtual device addressable
          through a target.

       LSB.  Least significant byte

       LSTTL.  Low power, Schotky transistor-transistor logic

       LUN.   Logical unit number, an encoded 3-bit identifier
          for the logical unit.

       C.  Microcomputer

       computer.  Microcomputer

       MFM.  Modified frequency modulation (encoding)

       MO.  Magneto optics

       MSB.  Most significant byte

       MSG.  Message

       MTBF.  Mean time between failures

       MTTR.  Mean time to repair

       MZCAV.  Maxtor Zoned Constant Angular Velocity (format)

       N.C.  No connection

       negate.  A signal driven to the false state

       nom.  Nominal

       OEM.  Original equipment manufacturer

       one.  True signal value

       parity.   A method  of checking  the accuracy of binary
          numbers
       PC.  Polycarbonate
       PCB.  Printed circuit board

       peripheral device.   A  peripheral that can be attached
          to a SCSI device

       PLL.  Phase-locked loop

       PLO.  Phase-locked oscillator

       PM.  Preventive maintenance

       P/N.  Part number

       POH.  Power On hours

       P-P.  Peak to peak

       PROM.  Programmable read only memory

       PTRN.  Pattern

       RAM.  Random-access memory

       reconnect.   The function  that occurs  when  a  target
          selects an  initiator to continue an operation after
          disconnect.

       req.  Request

       reserved.  Bits, bytes, fields and code values that are
          set aside for future standardization.

       RLL.  Run-length limited

       ROM.  Read-only memory

       rsrv.  Reserved

       R/W.  Read and/or write

       SCSI.  Small Computer Systems Interface

       SCSI address.   The  octal representation of the unique
          address (0 - 7) assigned to a SCSI device.

       SCSI ID.   The  bit-significant representation  of  the
          SCSI address,  referring to  one of the signal lines
          DB (7 - 0).
       status.   One byte of information sent from a target to          an initiator
upon completion of each command.

       STD.  Standard

       SW.  Software

       sync.  Synchronization, synchronous

       target.   A SCSI  device  that  performs  an  operation
          requested by an initiator, in this manual, usually a
          disk drive.

       tbd.   To be  determined.  Values which are not defined
          as of the date this manual is published.

       TLA.  Top level assembly

       TTL.  Transistor-transistor logic

       typ.  Typical

       UL.  Underwriter's Laboratories, Inc.

       UNC.  Unified National Coarse

       UNF.  Unified National Fine

       VDE.  Verband Deutscher Electrotechniker

       vendor unique.   The  bits, fields, or code values that
          are vendor specific.

       WORM.  Write once read multiple

       XFER.  Transfer

       zero.  False signal code

Rev B								Anderson/Sandoval
10/16/93