Archive PYTHON 4322 User manual

PYTHONTM
DDS-DC DATA COMPRESSION
DAT TAPE DRIVES
Model: 4322 (3.50-lnch, Internal Tape Drive)
4542 (5.25-lnch, Internal Tape Drive)
4352 (External Subsystem)
PRODUCT DESCRIPTION MANUAL
January 1992
ARc ·
CORPO~J!~E:------------------------~

ARCHIVE PYTHONDDS-DC OAT DRIVES---PRODUCTDESCRIPTIONMANUAL
PYTHONlM
DDS-DC DATA COMPRESSION DAT DRIVES
4322: 3.5-lnch, Internal Tape Drive
4542: 5.25-lnch, Internal Tape Drive
4352: External Subsystem
PRODUCT DESCRIPTION MANUAL
,v-6
COfJft' .;(~~
ARCHIVE
CORPORATION
1650 SunflowerAvenue
Costa Mesa,
CA 92626
[phone]/FAX: [phone]
January 1992

ARCHIVE PYTHON DDS-DC DAT DRIVES---PRODUCTDESCRIPTION MANUAL
DATE
01/92
REVISION RECORD
REV
002
REVISED PAGES
i through viii, 1-1 through
1-3, 1-6, 1-8 through
1-11, 2-2, 2-4 through
2-6, 2-8, 2-9 and 2-10
deleted, 3-6, 3-10
through 3-12,
4-1 through
4-2, 4-10 through 4-11,
5-1, 5-4 through 5-8,
6-1 through 6-16, 7-3
7-8, 8-2 through 8-14,
9-1, A1-A3, C1, C-4
through C-7, C-10, C-12
ii
Manual Part Number 27296-002
Copyright 1991 and 1992Archive Corporation.
All rights reserved.
No part of this publication
may
be reproduced, stored in a retrieval system,
or transmitted, in any form or by any means,
electronic, mechanical, photocopying, recording
or otherwise, without prior written permission
from Archive Corporation.
Archive, Python, and QICstream are trademarks
of Archive Corporation.
Product features and specifications described in
this manual are subject to change without
notice. The manufacturer is not liable for any
damages
or for the loss of information resulting
from the performance or use
of the infonriation
contained herein_

ARCHIVE PYTHONDDS-DC OAT DRIVES---PRODUCTDESCRIPTION MANUAL
CONTENTS
Preface ........ .
Chapter 1. Introduction
1.1 Overview. . . .
1.2 Python Models. .
1.2.1 Python Model Numbers. .
1.2.2 Python OAT Drives
....
1.3 Features . . . . . . . . . . . . .
1.4 Typical System Configurations. .
1.5 OAT Technology Overview
..
1.5.1 Helical Scan Recording.
1.5.2 Tape Formats. . . . . .
1.5.3 Data Compression---General
1.5.4 Flash EEPROM.
1.6 Software ..... .
1. 7 About This Manual. .
Chapter 2. Specifications. . .
2.1 Overview
..... .
2.2 Physical Specifications.
2.3 Power Specifications. .
2.4 Drive Performance Specifications.
2.5 Environmental Requirements .
2.6 OAT Cassette Specifications.
2.7 Regulatory Compliance. .
Chapter 3. Installation. . . . . . . . . . .
3.1 Introduction . . . . . . .
....
3.2 Guidelines and Cautions (4322 and 4542 Internal Models)
3.3 Unpacking and Inspection . . .
3.4 Cabling and Connectors . . . . .
3.4.1 Cabling Considerations . .
3.4.2 Electrical Characteristics . .
3.4.3 Single-Ended SCSI Connector---Internal Models 4322 and 4542.
3.4.4 Single-Ended SCSI Connector---Model 4352
3.5 Installing the Python 4322 and 4542 Internal Drives.
3.5.1 Setting Operational Switches
3.5.2 Mounting the Drive Unit . . . . . . .
3.5.3 Completing Connections
.....
3.6 Installing the Python 4352 External Drive. .
3.6.1 Selecting the SCSI Address. . . .
3.6.2 Completing the Interface Connection .
3.6.3 Connecting the Power
Cord.
Chapter 4. Drive Operation . . . . .
4.1 Introduction . . . . . . . . .
4.2 Data Compression Operation.
iii
viii
1-1
1-1
1-3
1-3
1-4
1-6
1-7
1-8
1-8
1-8
1-9
· .1-10
· .. 1-10
.
... 1-11
2-1
2-1
2-1
2-4
2-6
2-7
2-7
2-8
3-1
3-1
3-1
3-2
3-2
3-2
3-2
3-3
3-4
· . 3-5
3-6
· .3-12
.3-15
.3-16
· .. 3-17
· .. 3-17
· .3-18
4-1
4-1
. 4-1

ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCTDESCRIPTIONMANUAL
4.3 Front Panel LED Operation . . . . . . . . . . . . . . . .
4.4 Loading/Unloading the Cassette. . . . . . . . . . . . . .
4.4.1 LoadinglUnloading a Cassette (Normal Operation) .
4.4.2 Unloading a Cassette (Manual Operation).
4.5 Using a Blank Cassette
...... .
4.6 Using a Cassette Containing Data . . . . . . . .
4.7 Using a Prerecorded Audio Cassette. . . . . . .
4.8 Loading Revised Firmware via Archive Firmware Cassette.
Chapter S. SCSI Interface
5.1 Introduction
....
5.2 SCSI-1 Interface ..
5.3 ANSI X3.131 Conformance Statement (SCSI-I).
5.4 SCSI-2 Interface ................ .
5.5 ANSI X3T9.2 Conformance Statement (SCSI-2) (Working Draft, Rev 10) .
Chapter 6. Tape Formats . . .
6.1 Introduction
..... .
6.1.1 DDS Format
..
6.1.2 DDS-DC Format ..
6.1.3 Commonalities Between the Formats.
6.2 Entities (DDS-DC Format Only)
..
6.3 Tape Layout ....... .
6.4 Single Data Space Layout. . . . .
6.4.1 Device Area
...... .
6.4.2 Reference and System Area.
6.4.3 Data Area . . . . . . . .
6.4.4 End-of-Data (EOD) Area
..
6.5 Two-Partition Layout ....
6.6 Data Storage Organization. .
6.7 Individual Track Layout.
6.7.1 Main
Area.
6.7.2 Subareas. . . . .
6.8 Group Structure. . .
6.8.1 Data Frames . .
6.8.2 Index. . . . . .
6.8.3 ECC Frame. . .
6.8.4 Amble Frames .
6.9 Indexing. . . . . . . . .
6.9.1 Group Information Table (GIT)
..
6.9.2 Block Access Table (BAT). .
6.10 Vendor Group .. .
6.11 Read-After,Write
.. .
Chapter 7. Data Compression.
7.1 Introduction
..... .
7.1.1 Data Compression Considerations
7.1.2 DCLZ Algorithm
....
7.1.3 Hardware Compression.
7.1.4 Data Integrity ...... .
iv
· .4-2
· .4-5
.4-5
· .4-6
· .4-9
.4-10
.4-10
.4-11
· .5-1
.5-1
· .5-1
.5-4
· .5-5
· .5-7
· .6-1
· .6-1
.6-1
· .6-2
· .6-2
· .6-3
· .6-4
· .6-4
· .6-5
· .6-5
· .6-7
· .6-7
· .6-7
· .6-8
· .6-9
· .6-9
.6-10
. . 6-11
· 6-12
.6-12
.6-12
· 6-13
· 6-13
· 6-13
.6-14
· 6-15
6-16
· .7-1
· .7-1
· .7-1
· .7-2
· .7-3
· .7-3

ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCTDESCRIPTIONMANUAL
7.2 DCLZ Algorithm ............ .
7.2.1 Simplified Compression Operation
7.2.2 Dictionary. . . . . . . . . . . . . .
7.2.3 Simplified Decompression Operation .
7.3 AHA3101 Data Compression
Chip. .
Chapter 8. Theory of Operation. .
8.1 OvelView. . . . . . . . .
8.2 Block Diagrams . . . . . .
8.3 Python DDS-DC DAT Drives
8.3.1 Helical Scan Recording
-- Four-Head Design.
8.3.2 Motors and Control Circuits.
8.3.3 Flash EEPROM. .
8.3.4 Sensors
...... .
8.3.5 Audio Output Jack
8.4 DAT Cassette . . . . . .
Chapter 9. Maintenance and Reliability.
9.1 Maintenance .......... .
9.1.1 Head Cleaning
..... .
9.1.2 Automatic Drive Spin-Down and Write
..
9.1.3 Guidelines for High Temperature or Humidity Conditions.
9.2 Reliability . . . . . . . . . . . . . . .
9.2.1 Mean-Time-Between-Failure .
9.2.2 Mean-Time-To-Repair
Appendix A. Glossary of Terms . . .
Appendix B. Acronyms
and Measurements . .
B.1 Abbreviations and Acronyms ...
B.2 Measurements. . . . . . . . . . . . .
Appendix C. Data Compression---SCSIInformation ..... .
C.1 Introduction . . . . . . . . . . . . . .
C.2 MODE SELECT Page. . . . . . . . . . . .
C.2.1 Compression Control---Byte 02
..
C.2.2 Decompression Control---Byte 03.
C.3 MODE SENSE Page
........... .
C.3.1 Compression Control---Byte 02
..
C.3.2 Decompression Control---Byte 03.
C.3.3 Compression Algorithm---Byte 07 .
C.3.4 Decompression Algorithm---Byte
11 .
C.4 Request Sense Data . . . . . . . . . . . .
C.5 Implementation Notes . . . . . . . . . . .
7-4
7-4
7-5
· . 7-6
7-7
8-1
8-1
8-2
...... 8-2
8-7
· . 8-8
· .. 8-10
· .. 8-10
· .8-10
.8-11
· 9-1
9-1
9-1
9-2
9-2
9-3
9-3
9-3
..... A-I
· B-1
· . B-1
· . B-2
· C-l
· C-l
· . C-l
· .. C-2
· C-2
· . C-4
· .. C-S
· C-5
· . C-6
· C-6
. . .
.. .. C-6
...... C-7
C.5.l Retrieval
of Compressed Data from Noncompressing Modes . · . C-7
C.S.2 SCSI Command Operation for Noncompressing
Modes.
C.6 WRITE DATA BUFFER (3Bh) ............... .
C.6.l WRITE DATA BUFFER Command Descriptor Block
C.6.2 Command Descriptor Block Field Descriptions .
C.6.3 WRITE DATA BUFFER Data Header
C.6.4 Completion Status . . . . . . . . . . . . . . . .
v
· . C-9
.
....... C-lO
· .C-lO
· .. C-ll
. ... C-ll
· .. C-l2

ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCTDESCRIPTION MANUAL
Figure 1-1. Python 4322 OAT Drive ..
Figure 1-2. Python 4542 OAT Drive.
Figure 1-3. Python 4352 OAT Drive.
FIGURES
Figure 1-4. SCSI System Sample Configurations.
Figure 2-1. Python 4322 OAT Drive General Dimensions
...
Figure 2-2. Python 4542 OAT Drive General Dimensions.
Figure 2-3. Python 4352 External Subsystem General Dimensions .
Figure 3-1. Python 4322 Switchbank
Access.
Figure 3-2. Python 4542 Switchbank Access.
1:; .... " .. "" 'l. 'l. T'''D (;:""tr-h n .. f'<llllt c;;: ..tt1nO'c:
... .IoU.\,., -'--'- ~.a..I.. \..1 ..... "".1.1. ..,"" ............ ~"" ..... .&.b- •••
Figure 3-4. SCSI Device Address Selection (4322 and 4542) .
Figure 3-5. JP6 External SCSI Address Port .
Figure 3-6. Mounting Hole Locations (4322). . . . . . . . .
Figure 3-7. Mounting Hole Locations (4542). . . . . . . . .
Figure 3-8. Power and SCSI Connectors---4322 OAT Drive
Figure 3-9. Power and SCSI Connectors---4542 OAT Drive
Figure 3-10. Python 4352 Rear Panel
..
Figure 3-11. Daisy chain Diagram ...
Figure 4-1. Python 4322 Front Panel.
Figure 4-2. Python 4542 Front Panel.
Figure 4-3. Python 4352 Front Panel .
Figure 4-4. Cassette Loading (4322 OAT Drive)
..
Figure 4-5. Manually Removing a Cassette---Python 4322 Drive ..
Figure 4-6. Manually Removing a Cassette---Python 4542 Drive ..
Figure 4-7. Manually Removing a Cassette---Python 4352 Drive ..
Figure 6-1. Single Data space Tape Layout ....
Figure 6-2. Reference and System Area Layout.
Figure 6-3. Two-Partition Tape Layout
..
Figure 6-4. Individual Track Layout . . . . . . .
Figure 6-5. Group Structure
.......... .
Figure 6-6. Group Structurc---DDS and DDS-DC Formats
..
· .1-4
· .1-5
· .1-5
.1-7
· .2-2
· .2-3
· .2-3
.3-6
· .3-7
,3-8
.3-9
· 3-12
· 3-13
.3-14
· 3-15
· 3-16
.3-17
. . 3-18
· .4-3
· .4-3
· .4-4
· .4-5
· .4-7
. .... 4-8
.4-9
· .6-5
· .6-6
.6-8
· .6-9
.
... 6-11
.6-12
Figure R-l. Simplified Block Diagram -- Python DDS-DC Drives. . .8-3
Figure 8-2. Block Diagram -- SCSI Controller Python Models 4322NT and 4542NT
DDS-DC Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ..8-4
Figure 8-3. Block Diagram -- SCSI Controller Python Models 4322NP, 4542NP, and 4352XP
DDS-DC Drives . . . . . S-5
Figure 8-4. Python State Diagram . . . .. 8-6
Figure 8-5. Four-Head Design . . . . .8-7
Figure 8-6. Alternate Azimuth Angles . .8-8
Figure 8-7. OAT Cassette . . . . . . . 8-11
Figure 8-8. Cassette Design Features. . 8-12
vi

ARCHIVE PYTHONDDS-DC OAT DRIVES---PRODUCTDESCRIPTIONMANUAL
Figure 8-9. Write-Protect Tab on DAT Cassette.
Figure C-1. LBAs
of Tape inExample. . .
TABLES
Table 1-1. Python DDS-DC SCSI DAT Models---Cross Reference
Table 1-2. Chapter Descriptions. . . . . . . . . . . . . . .
Table 2-1.
Table 2-2.
Table 2-3.
Table 2-4.
Table 2-5.
Table 2-6.
Table 2-7.
Physical Specifications for Python DAT Drives.
Power Specifications for the 4322 and 4542 Drives ..
Power Connector PinAssignments (Models 4322 and 4542) . .
Power Specifications for the Python 4352 Drives. . . . . . .
Perfonnance Specifications: Python DDS-DC DAT Drive (Data
Compression Enabled)
.............. .
Environmental Specifications: Python DDS-DC Drives
Regulatory Compliances
................ .
Table 3-1. Single-Ended SCSI Connector Pin Assignments: Models 4322 and 4542.
Table 3-2. Single-Ended SCSI Connector Pin Assignments: Model 4352 .
Table 4-1. LED Summary. .
Table 5-1. Status Codes---SCSI-l
..
Table 5-2. Message Codes---SCSI
-1. .
Table 5-3. Commands---SCSI-l.
Table 5-4. Status Codes---SCSI-2
..
Table 5-5. Message Codes---SCSI-2. .
......
Table 5-6. Commands---SCSI-2.
Table 6-1. Bit configurations
of Flag Byte (DDS-DC Fonnat Only) .
Table 7-1. Simplified Compression
...
Table 7-2. Simplified Decompression.
Table 7-3. Dictionary. . . . . . . . .
Table 8-1. Tape Lengths and Capacities. . .
Table 9-1. Reliability Specifications. . . .
· .8-13
· . C-8
.... 1-3
. .. 1-11
· 2-2
· 2-4
2-5
2-5
2-6
2-7
· 2-8
· 3-4
3-5
4-4
· 5-1
· 5-2
5-3
.
... 5-5
5-5
5-6
· .6-15
· 7-4
7-6
7-7
.8-12
· . 9-3
Table C-1. Data Compression MODE SELECT
Page. . . . C-l
Table C-2. DDE and RED Bit Configurations. . . . . . . . . . . . . . . . C-3
Table C-3. Algorithms---MODE SELECT Page. . . . . . . C-4
Table C-4. Data Compression MODE SENSE
Page. . . . . C-4
Table C-5. Algorithms---MODE SENSE Page. . . . . . . C-6
Table C-6. Sense Data Values and Descriptions. . . . . . . . . C-7
Table C-7. Command Descriptor Block: WRITE DATA BUFFER
.. C-I0
Table C-8. Field Descriptions: WRITE DATA BUFFER Command Descriptor Block. . . .C-ll
Table C-9. Data Header: WRITE DATA BUFFER . . . . . . .. C-ll
Table C-I0. Completion Status: WRITE DATA BUFFER .................. C-12
vii

ARCHIVE PYTHONDDS-DC OAT DRIVES---PRODUCTDESCRIPTION MANUAL
PREFACE
The Archive Python™ DDS-DC Digital Audio Tape (DAT) products---Models 4322NT, 4322NP, 4542NT,
4542NP, and 4352XP---are computer DAT drives with data compression. These drives also contain an
embedded Small Computer System Interface (SCSI) controller that provides a single-ended
SCSI-lor
SCSI-2 interface.
The 4322 models are 3.5-inch, internal drives. The 4542 models designate 5.25-inch versions
of these
3.5-inch internal drives, factory-built with a 5.25-inch bezel and mounting rails. The 4352 model is a self-
contained, external subsystem with power supply.
The 4-digit, 2-letter model numbers used for Python DAT drives are explained in Section 1.2.1.
In this
manual, the short, 4-digit model designation (4322, for example) refers to all
of the 4-digit,
2-letter models included in that model designation. For example, 4322 refers to the 4322NT and 4322NP
models.
This document gives you an in-depth look at the Python 4322, 4542, and 4352 DDS-DC drives. It
is intended
for those familiar with basic tape drive technology or who are using or evaluating Python DAT data
compression drives.
This manual contains all the technical information pertinent to the internal and external Python DDS-DC
DAT drives except for details of the SCSI-l and SCSI-2 interfaces. Detailed technical information about the
Python SCSI interfaces (including a complete command summary) is contained in the Python Technical
Reference Manual (PIN 25356-002; DDS SCSI commands only) or the Python SCSI Manual (pIN
27298-001) available in 1992. However, Appendix C of this manual provides specific, important SCSI
information pertaining to data compression.
IJD
viii

1.1 Overview
CHAPTER 1
INTRODUCTION
INTRODUCTION
Archive Python Digital Audio Tape (DAT) drives are designed for computer environments requiring high
performance, high capacity data storage. Based on a proven 3.5-inch mechanism, the Python drives
described here---Models 4322NT and 4322NP (3.5-inch), 4542NT and 4542NP (5.25-inch), and 4352XP
(external)---provide hardware data compression which supports the industry standard Digital Data Storage
Data Compression (DDS-DC) format.
All Python data compression drives provide
an embedded, single-ended Small Computer Systems Interface
(SCSI) controller. The drives are equipped with either a 512 kilobyte (KB) on-drive buffer or a 1 megabyte
(MB) buffer
to facilitate efficient operation. In addition, the 4322NP, 4542NP, and 4352XP models offer
leading-edge electronically erasable, programmable, read-only memory (flash EEPROM), which enables
qualified Archive OEMs
to download revised firmware to the drive via three methods: using the Python
drive's serial port, the SCSI bus, or a specialized Archive firmware cassette.
The Python DDS-DC drives comply with the American National Standards Institute (ANSI) and European
Computer Manufacturers Association (BCMA) DDS format, which ensures interchange compatibility
of
digital data stored on a small removable DAT cassette (approximately 2 inches x 3 inches x 0.4 inch) using 4
mm tape. The Python data compression drives also comply with the ANSI/ECMA Digital Data Storage Data
Compression (DDS-DC) format, which
is the industry standard format for DAT data compression and is a
superset
of the DDS format. These Python drives use an advanced DCLZ (data compression LempelZiv)
algorithm
to compress data by up to four or more times. More importantly, however, DDS-DC data
compression
is transparent to the host software and SCSI driver, enabling rapid integration and preserving
existing software investments.
Because the DDS-DC format
is a superset of the DDS format, the Python data compression drives are fully
compatible with the DDS format for reading and writing standard, uncompressed data. To switch operation
from compressed to uncompressed mode, the host computer can issue a SCSI command. On internal Python
DDS-DC models, a hardware switch
is also available to enable or disable the DDS pass-through
(uncompressed) mode as an initial power-on default.
Tape capacity and sustained data transfer rate using DDS-DC are dependent upon the characteristics
of the
files being compressed, along with other parameters, including the speed
of the host system, and the
operating system
and application software used. Nevertheless, Archive Python DDS-DC drives typically
provide a doubling
of storage capacity and transfer rate---and a maximum quadrupling of storage capacity
and transfer rate---when compared with computer DAT drives without data compression. That is, Python
data compression drives provide a typical 2.6 gigabyte (GB) storage capacity on a 60-meter DDS data
cassette and 4.0 GB on a 90-meter DDS data cassette. The drive sustained transfer rate at this typical 2:1
compression ratio
is 366 kilobytes/second (KB/sec), or 22 megabytes/minute (MB/minute).
With highly redundant files, such
as many database files, Python DDS-DC drives can achieve a 4:1
compression ratio which provides a nominal maximum storage capacity of 5.2 GB on a 60-meter DDS data
1-1

ARCHIVE PYTHONDDS-DC OAT DRIVES---PRODUCTDESCRIPTION MANUAL
cassette and 8.0 GB on a 90-meter DDS data cassette. The transfer rate at this 4:1 compression ratio is 732
KB/sec (44 MB/min). Although this 4:1 compression ratio (and corresponding 8.0 GB capacity and 44
MB/minute transfer rate) is termed a "maximum", these values are a nominal maximum only for the more
conventional file types. With more highly redundant data, Python DDS-DC drives are capable
of much
higher compression ratios, capacities, and transfer rates.
Python DDS-DC drives combine inherent DAT technology and DDS-DC data compression capabilities with
Archive's proven computer grade design to provide unmatched reliability and performance characteristics
among DDS products. These drives are ideal for PC, workstation, network, and minicomputer applications
such as:
o Backup of high capacity fixed disks.
o Data interchange between systems.
o Software distribution.
o Online data collection.
o Direct-access secondary storage for text, graphics or multimedia information of all types.
o Archival storage.
Built using long-wearing materials and custom Large Scale Integration (LSI) components, the Python
3.5-inch SCSI DAT drive used in all these DDS-DC models was engineered for heavy-duty computer
applications. Providing carefully controlled tape handling and rapid, smooth operation, the Python design
promotes long life for key components such as the rotating DAT drum, drive heads, and the media itself. One
major benefit of this new, computer grade engineering is low power consumption -- typically below 7 Watts.
All Python DDS-DC drives contain an embedded SCSI controller that supports SCSI-1 (ANSIX3.131, 1986)
and SCSI-2 (ANSI X3T9.2 Working Draft, Revision 10). The 3.5-inch and 5.25-inch internal drive form
factors are tailored for easy installation in today's computers, and the full-featured embedded SCSI controller
facilitates easy integration into a variety
of systems. The internal models (4322 and 4542) are hardware
switch-selectable for SCSI-1 or SCSI-2, and all models are software selectable for SCSI-1 or SCSI-2. The
Python DDS-DC drives also provide synchronous or asynchronous SCSI and a high speed burst rate of 5
MB/second.
Python DDS-DC products provide unmatched reliability through three levels of error correction code (BCC)
and the four-head design, which allows read-after-write (RAW) error detection and correction. Python
internal data compression models also contain an onboard serial port that provides the capability for
extensive testing
of the Python drives.
All Archive Python drives comply with the DDS tape format standard---American National Standard
Helical-Scan Digital Computer Tape Cartridge 3.81 mm (0.150 in) for Information Interchange. The Python
drives are designed to use data-grade DDS DAT media, not audio DAT media, and provide maximum data
integrity and reliability with computer DAT cassettes officially qualified by Archive.
The Archive-qualified
Model M31300 DDS data cassette (60 m), Model M32000 DDS data cassette (90 m), and M7301 DDS head-
cleaning cassette (or equivalents supplied by Archive subsidiary companies) are recommended.
1-2

INTRODUCTION
1.2 Python Data Compression Models
The Python SCSI drives with data compression are as follows:
o 3.5-inch, half-high DDS-DC DAT drives that mount internally (Models 4322NT and 4322NP).
o 5.25-inch, half-high DDS-DC DAT drives that consist of a 3.5-inch drive with 5.25-inch mounting
rails and bezel that mount internally in a 5.25-inch half-high space (Models 4542NT and 4542NP).
o A complete external subsystem containing the 3.5-inch DDS-DC DAT drive and built-in worldwide
power supply (Model 4352XP).
Table
l-llists a cross reference of data-compression models and features.
Table 1-1. Python DDS-DC SCSI OAT Models--Cross Reference
FEATURE 4322NT 4322NP 4542NT 4542NP 4352XP
Buffer Size
512 KB PIN 259n-Oxx PIN 27264-Oxx PIN 27402-Oxx PIN 27373-Oxx PIN 27265-Oxx
1024
KB
PIN 25977-5xx PIN 27264-5xx PIN 27402-5xx PIN 27373-5xx PIN 27265-5xx
Form Factor 3.50"
H.H.
3.50" H.H.
5.25" H.H,<1)
5.25" H.H.(1)
External Subsystem
Mounting Internal Internal Internal Internal External
SCSI Single-Ended Single-Ended Single-Ended Single-Ended Single-Ended
Data
Compression Yes Yes Yes Yes Yes
Conventional
EEPROM Yes No Yes No No
Flash
EEPROM No Yes No Yes Yes
(1) 3.5" H.H. drive in 5.25" bezel and mounting rails.
NOTES: Certain part numbers listed may be available only as a special order.
Part numbers listed are for genericArchive Python DDS-DC OEM products only. Contact your distributor
or dealer for the correct distribution part numbers for ordering information.
1.2.1 Python Model Numbers
The six-position model numbers assigned by Archive to Python drives denote specific information as
follows:
12345 6
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ARCHIVE PYTHON DDS-DC DAT DRIVES---PRODUCTDESCRIPTION MANUAL
Position 1 shows the tape drive type. This character is always 4 for Archive DAT products, which refers to
the 4-millimeter tape size.
Position 2 shows the fonn factor. This character is either a 5, which refers to the 5.25-inch internal fonn
factor, or a 3, which refers to either the 3.5-inch internal fonn factor or an external Python subsystem, which
(like all Archive Python drives) uses a 3.5-inch internal mechanism.
Position 3 is a marketing option.
Position 4 denotes the following: 0 for single-ended SCSI interface models without data compression; 1 for
differential SCSI interface models without data compression; and 2 for single-ended SCSI interface models
with data compression.
Position 5 also shows whether the drive is an internal or external unit. This character is an N for internal or
an X for external.
Position 6 shows the interface and PROM type. For the SCSI-l or SCSI-2 compatible interface (default
setting SCSI-2) with the standard PROM, this character
is a T. For the SCSI-l or SCSI-2 compatible
interface (default setting SCSI-2) with flash EEPROM, this character
is a P.
1.2.2 Python OAT Drives
Figures 1-1, 1-2, and 1-3 illustrate the Python 4322, 4542, and 4352 drives, respectively.
Figure
1-1
Python 4322 OAT Drive
1-4

Figure 1-2
Python 4542 DAT Drive
Figure 1-3
Python 4352 DAT Drive
1-5
INTRODUCTION

ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCTDESCRIPTION MANUAL
1.3 Features
The Python data compression drives embody Archive's commitment to engineering reliable and durable tape
drive products
which implement leading-edge technology. In summary form, key features of the Python
DDS-DC drives are:
o All Python DDS-DC drives based on proven 3.5-inch Python DAT drive, with the identical drive
mechanism used in standard (non-compressed) Python products
o 3.S-inch internal form factor for installation in a 3.S-inch half-high space (Model 4322NT and
4322NP)
o 3.S-inch DAT drive with factory-installed S.25-inch mounting rails and bezel for installation in a
S.25-inch half-high space (Models 4S42NT and 4S42NP)
o External subsystem with built-in, auto-sensing, worldwide power supply (Model 4352)
o Advanced onboard DDS-DC hardware using DCLZ (Data Compression LempelZiv) data
compression algorithm
o ANSI/ECMA DDS and DDS-DC tape format compliance for compatibility and interchange
o Reads and writes both DDS uncompressed and DDS-DC compressed data and data cassettes
o Typical capacity of 4 GB, nominal maximum capacity of 8 GB on a 90-meter DDS cassette
o High speed random access of 20 seconds (average) to any file on a 60 m tape; 30 seconds for a
90 m tape
o High speed transfer rates for fast backups:
-- 183 KB/sec (11 MB/min)---uncompressed data
-- 366 KB/sec (22 MB/min) typical---compressed data
-- 732 KB/sec (44 MB/min) nominal maximum---compressed data
o High performance SCSI burst transfer rate of S MB/sec with up to 1 MB on-drive data buffer to
facilitate the
most efficient use of the host computer
o Four-head design with RAW error detection and rewrites
o Three levels ofECC to ensure data integrity
o Uncorrectable error rate ofless than 1 in 1015 bits
o Flash EEPROM ("NP" and "XP") models enable electrically upgradeable drive firmware
o Custom Archive designed LSI circuitry to reduce component count and boost drive reliability
o Advanced, single-chip, DAT formatter LSI
o Low power consumption---Iess than 7 Watts (typical) for internal drives
o Single-ended SCSI connection with these features:
-- Embedded full LSI, high speed SCSI controller
-- Switch selectable SCSI-1 or SCSI-2 interface on internal models (as default setting at power up)
for flexibility in system integration
-- Software selectable SCSI-1 or SCSI-2 interface on all models
-- Software selectable synchronous or asynchronous SCSI data transfer
1-6

INTRODUCTION
-- Onboard outputjack on internal models for configuring the SCSI address if repackaged in an
external box
-- Compatibility with the Archive SCSI Viper quarter-inch cartridge drives
o Onboard serial port for internal diagnostics (internal models only---4322 and 4542)
o Automatic power-on selftests (switch option on internal models)
o Manual emergency cassette ejection procedure
1.4 Typical System Configurations
The SCSI standard supports up to eight SCSI addresses or IDs. These IDs refer to host adapters or peripheral
devices such as printers, magnetic disks, or tape drives. The eight devices or hosts are daisy chained together.
Figure 1-4shows sample configurations
of SCSI systems.
COMPUTER HOST
~ SCSI BUS
.....
PYTHON
SYSTEM ADAPTER
~
~
DRIVE
SINGLE INITIATOR -SINGLE TARGET
COMPUTER HOST
~ SCSI BUS
.....
PYTHON
SYSTEM ADAPTER
~ JIll""
DRIVE
SINGLE INITIATOR
-SINGLE TARGET MAGNETlC
.....
DISK,
JIll""
PRINTER,or
OPTlCAL
DISKS
COMPUTER
HOST
...... SCSI BUS
......
PYTHON
SYSTEM ADAPTER
......
~
DRIVE
MAGNETlC
.......
DISK,
.....
PRINTER,or
OPTICAL
DISKS
MAGNETlC
.....
DISK,
-".
PRINTER, or
OPTICAL
DISKS
MAGNETIC
COMPUTER
HOST
~
.....
DISK,
PRINTER,or
SYSTEM ADAPTER
~
."",..
OPTICAL
DISKS
SINGLE INITIATOR
-SINGLE TARGET
Figure 1-4
SCSI System Sample Configurations
1-7

ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCTDESCRIPTION MANUAL
1.5 OAT Technology Overview
First developed for the audio electronics market, DAT technology was first applied in computer peripherals
in the late 19808. Unlike traditional magnetic tape audio cassette products, DAT technology proves
inherently reliable through the helical scan recording method, which provides a high recording density with
a very low error rate. All DAT products, including computer implementations, use the helical scan recording
method. This recording method has been used in professional video tape recorders (VTRs) since 1956 and in
home video cassette recorders (VCRs) since 1974. In 1986, DAT products using helical scan technology
were first developed for audio applications. DAT consumer products are specifically designed for digital
audio recording and playback and compete with such products as analog audio cassette decks and compact
disk (CD) players.
1.5.1 Helical Scan Recording
Helical scan recording was originally developed as method of efficiently recording high-quality television
signals on a relatively slow moving tape.
It requires that both the tape and the recording head move
simultaneously. This recording method results in an extremely high recording density, far higher than can be
achieved with stationary-head devices such
as 1I2-inch open-reel or 1/4-inch cassette tapes. (See Chapter 8,
"Helical Scan Recording -- Four-Head Design" for additional information.)
In helical scan recording, both the read and write heads are located on a rapidly rotating cylinder or drum.
The cylinder
is tilted at an angle in relation to the vertical axis of the tape. As the tape moves horizontally, it
wraps around the part
of the circumference of the cylinder (900) so that the head enters at one edge of the
tape and exits at the other edge before the tape unwraps.
The horizontal movement
of the tape in combination with the angular movement of the cylinder causes the
track to
be recorded diagonally across the tape rather than straight down its length. The resulting recorded
track, nearly one inch, is approximately eight times longer than the width
of the tape.
1.5.2 Tape Formats
Archive Python DDS-DC drives are designed to use the industry standard DDS and DDS-DC tape formats.
These two formats are summarized in the following text.
DDS Tape Format
This standard fonnat was codeveloped by DDS manufacturers to support DAT devices as computer
peripherals. The objectives
of DDS are to maximize storage capacity and performance; to facilitate data
interchange; to provide compatibility with existing tape storage command sets; and to provide extremely fast
random access. The DDS format also takes advantage
of the helical scan recording method and the inherent
error correction capability
of the DAT technology to augment error detection and correction.
The format consists of a finite sequence of data groups with each data group being a fixed-length recording
area. A data group is made up
of 22 data frames and 1 ECC frame; each frame is made up of two helical
scan tracks. The advantages
of the fixed-length data group is that ECC is easily generated, and buffering
requirements are simplified. (See Chapter 6, "Tape Formats", for additional information.)
1-8

INTRODUCTION
Although data groups are fixed-length and always contain 22 data frames, the DDS format is designed such
that variable-length computer records can be stored in the fixed-length data groups.
The native transfer rate
of 11 million bytes/minute (183 KB/sec) is a characteristic of the DDS format for
computer OAT technology. At this transfer rate, a full 1.3 GB
of information can be written in 120 minutes,
and a full 2.0 GB
of information can be written in 180 minutes. Another important speed consideration is that
once the information
is written, specific files or data sets can be located at up to 200 times the speed at which
they were originally written. The resulting average time to randomly access any file on a 60-meter OAT
cassette
is 20 seconds.
DDS-DC Tape Format
A superset of the basic DDS OAT format, DDS-DC drives can write compressed and uncompressed data to
the same cassette. Thus, because DDS-DC
is based on the DDS format, backward compatibility is
maintained.
Introduced by the DDS Manufacturers Group and approved by ANSI and ECMA, DDS-DC
is a record
compression industry-standard format that provides support for loss
less compression algorithms based on
substitution---such as those
of the Lempel-Ziv family.
This format supports compressed and uncompressed records. A recorded OAT cassette may contain
compressed records, uncompressed records, filemarks, and setmarks. Compressed records exist within
recorded objects called entities. Entities and uncompressed records are collected into groups.
Many aspects
of the DDS-DC format are identical to those of the DDS format:
o The series of transformations (randomizing, interleaving, generation and inclusion of two Reed-
Solomon error-correcting codes, and etc.) applied to a group before recording
o The tape layout
o The third group-based level of Reed-Solomon error-correcting codes (C3)
The only differences between the DDS and DDS-DC formats are in the contents
of the groups.
The combination
of OAT technology and the DDS-DC format provides a solid core around which computer
OAT drives with exceptional performance and reliability can be designed, such
as the Python data
compression
prodUCts.
1.5.3 Data Compression---General
Data compression is based on reducing the redundancy that occurs naturally in data streams of text, graphics,
code, and other data. Reducing or eliminating such redundancy prior to recording the information to tape
significantly increases the amount
of data that can be recorded on a given amount of tape.
Data compression causes repeated strings
of data to be recognized and replaced by symbols or codewords
that encode the strings or point back
to the original occurrence of the string. In this way, data compression
uses fewer characters to represent the original data.
1-9

ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCTDESCRIPTION MANUAL
The Lempel-Ziv (LZ) algorithms are a family of string-based compression algorithms developed in the late
1970s by Messrs Lempel and Ziv. The Python DDS-DC DAT drives use the DCLZ algorithm, which is
based on a Lempel-Ziv algorithm that was enhanced by WeIch. DCLZ builds a symbol dictionary that
represents data strings identified as repeated events in incoming data.
The algorithm then writes the symbols
to the tape. This compressed data is then decompressed with the original data strings resubstituted for the
symbols from the dictionary when the data is read back. (See Chapter 7, "Data Compression", for detailed
information about the algorithm.)
1.5.4 Flash EEPROM
Another technological advancement incorporated into the Python 4322NP, 4542NP, and 4352XP drives is
flash
EEPROM, which is useful should the drive's SCSI firmware need to be upgraded at some point. With
the permanently installed, electrically upgradeable, flash
EEPROM memory, revised SCSI firmware for the
Python drive
can be loaded into the drive via anyone of three methods:
o Archive OEM firmware cassette (See Section 4.8.)
o Host SCSI bus
o Python drive serial port (internal drives) (See Chapter 8.)
This feature enables qualified Archive
OEMs needing to revise DDS-DC drive SCSI firmware to do so
rapidly and at a reduced cost. Flash
EEPROM should also prolong the life cycle of a drive because many
new techniques---such as increasing the capacity of the drive through support for ionger tapes---may require
only a firmware upgrade.
1.6 Software
One of the most cost-effective uses of DAT drives is to back up fixed disks. The software required to
perform a disk backup runs under the control
of the host computer's operating system. Compatibility with a
wide range
of software is also an important consideration in system integration. The Python DDS-DC
computer DAT drives are designed to take advantage of the host computer's standard magnetic tape backup
software or, optionally, to use backup software provided
by Archive and other suppliers.
These
Python drives comply with the QIC-I04 standard ensuring compatibility with the Archive Viper and
other quarter-inch cartridge software. (python drives maintain full SCSI-interface compatibility with the
Archive Viper
SCSI 150-MB quarter-inch cartridge prodUCt.) Also, use of variable-length records and the
ability to overwrite previously recorded data allow the Python drives to run software originally written for
l/2-inch reel-to-reel tape backup.
Standard Python
DDS drives have been proven compatible with an exceptionally wide range of SCSI host
adapters and interfaces, and network, operating system, and application software.
A major advantage
of DDS-DC data compression is that it is software transparent. Software transparency
means that, generally,
no modification is required to network, operating system, application, and device
driver software already proven compatible with Python
DDS drives to run with Python DDS-DC products.
1-10

INTRODUCTION
1.7 About This Manual
The remaining chapters and the appendices in this manual are briefly described in Table 1-2. A glossary of
terms is also included.
Table 1-2. Chapter Descriptions
NUMBER
TlT1..E
DESCRIPTION
2 Specifications
3 Installation
4 Drive Operation
5 SCSI Interface
6
Tape Formats
7 Data Compression
8 Theory of
Operation
9 Maintenance
and Reliability
Contains physical, performance, environmental, power, drive
tape handling, and OAT cassette specification tables. Also,
contains the SCSI-1 and SCSI-2 conformance statements.
Provides cautions, unpacking tips, inspection information, and
installation/connection steps including cabling requirements and
connector pinouts.
Explains the simple operation ofthe DDS-DC drives.
Lists general information about
the SCSI-1 and SCSI-2
interfaces. (See NOTE below.)
Explains
the DDS and the DDS-DC tape formats.
Describes the
data compression algorithm and explains pertinent
information for effective use of data compression.
Details the functional operation of various assemblies
ofthe Python DDS-DC drives.
Presents maintenance procedures and reliability
information.
AppA Glossary Defines key terms.
App8 Acronyms and
Measurements
AppC Data Compression
---SCSI Information
Lists the acronyms and measurements used in the manual.
Describes the specific SCSI information that pertains
to data compression
NOTE: This manualprovides all technical information about the Python 4322, 4542, and
4352 drives for hardware and software development and integration exceptcomplete
SCSI information on the SCSI-1 andSCSI-2 commands themselves. Refer to the
Python TechnicalReference Manual (PIN25356-002, DDS-only) or the Python SCSI
Manual (PIN27298-001) for detailed information about the SCSI interface, including
a complete commandsummary. Appendix C, however, doesprovide important,
specifIC SCSI informationpertaining to data compression. .
1-11