Quantum lto 4 Betriebsanweisung

Chapter 4  Theory

Data Compression

LTO-4 Half-Height Tape Drive User’s Guide

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data to be recorded in a fewer number of bits. These codewords or 

symbols point back to the original data string, using fewer characters to 

represent the strings. Because these smaller symbols are substituted for 

the longer strings of data, more data can be stored in the same physical 

space.
Some important benefits result from data compression in tape drives:

• 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.

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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