Data Compression - Sony DDS-4 Product Description Manual

4. OPERATION

4. 6 DATA COMPRESSION

The tape capacity is increased by compressing data prior to writing it to the tape. Data compression is a well established
technology for reducing the number of bits used to represent data in order to improve data transfer rate as well as reduce
the amount of storage space consumed by the data.
The SDT-10000/SDT-11000 uses the AK 8320 Data Compression IC from ASAHI KASEI MICROSYSTEMS. This
chip provides a powerful data compression algorithm in a very small package. The data compression used by the chip is
the DCLZ algorithm. DCLZ has been standardized (or is in the process of standardization) with the ANSI, ECMA and
ISO standards organizations. The DDS Manufacturers Group (made up of representatives from active DDS Format
Licensees) has agreed upon the DCLZ algorithm as the standard data compression algorithm for data interchange be-
tween DDS format drives.
The DC control page allows the host computer to enable data compression and also configure the way in which the drive
responds to compressed/uncompressed data boundaries on the tape.
Note: The DDS format allows both compressed and uncompressed data to reside on the same tape.
SDT-10000/SDT-11000 has a Dip switch to disable the Data Compression.
After power-on reset with this jumper set, data compression is disabled. However, a MODE SELECT command can
override the setting of this jumper.
After power-on reset without this Dip switch set, both data compression and data decompression are enabled. (See
3.1.5)
The more random the data is, the less compression is possible. This is due to the fact that data compression operates on
the principle of reducing the redundancy in the data string and random data has very little redundancy.
Data compression is a very powerful and reliable method increasing data capacity and transfer rate without compromis-
ing data reliability.
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