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Chapter 4 Theory

Data Compression

42 LTO-5 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

In an effective data-compression method, several factors are important:

• The amount of compression, which 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

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