Table of Contents
Advertisement
ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCT DESCRIPTION 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
Advertisement
Table of Contents
