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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
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