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Chapter 4 Theory
Data Compression
32 LTO-2 Half-Height Tape Drive User’s Guide
• The same amount of information can be stored on a smaller length of
tape.
• More data can be stored on a given length of tape.
• Performance can more closely parallel to that of high-transfer-rate
computers.
• More information can be transferred in the same time interval.
Data Compression
Considerations
4
In an effective data-compression method, several factors are important:
• The amount of compression. The amount of compression is measured
by the compression ratio. This ratio compares the amount of
uncompressed data to the amount of compressed data. It is obtained
by dividing the size of the uncompressed data by the size of the
compressed data)
• The speed with which data is compressed and decompressed relative
to the host transfer rate.
• The types of data to be compressed.
• The data integrity of the compressed data.
The amount of compression possible in a data stream depends on factors
such as:
• Data pattern
• Compression algorithm
• Pattern repetition length
• Pattern repetition frequency
• Object size (block of information to be compressed)
• Starting pattern chosen
The transfer rate depends on factors such as:
• Compression ratio
•Drive buffer size
• Host computer input/output (I/O) speed
• Effective disc speeds of the host computer
• Record lengths that the host computer transmits