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Concept
Gzip
Summary
gzip is a and a software application used for file compression and decompression. The program was created by Jean-loup Gailly and Mark Adler as a free software replacement for the compress program used in early Unix systems, and intended for use by GNU (from where the "g" of gzip is derived). Version 0.1 was first publicly released on 31 October 1992, and version 1.0 followed in February 1993.
The decompression of the gzip format can be implemented as a streaming algorithm, an important feature for Web protocols, data interchange and ETL (in standard pipes) applications.
gzip is based on the DEFLATE algorithm, which is a combination of LZ77 and Huffman coding. DEFLATE was intended as a replacement for LZW and other patent-encumbered data compression algorithms which, at the time, limited the usability of compress and other popular archivers.
"gzip" is often also used to refer to the gzip file format, which is:
a 10-byte header, containing a magic number (1f 8b), the compression method (08 for DEFLATE), 1-byte of header flags, a 4-byte timestamp, compression flags and the operating system ID.
optional extra headers as allowed by the header flags, including the original filename, a comment field, an "extra" field, and the lower half of a CRC-32 checksum for the header section.
a body, containing a DEFLATE-compressed payload
an 8-byte trailer, containing a CRC-32 checksum and the length of the original uncompressed data, modulo 232.
Although its file format also allows for multiple such streams to be concatenated (gzipped files are simply decompressed concatenated as if they were originally one file), gzip is normally used to compress just single files. Compressed archives are typically created by assembling collections of files into a single archive (also called ), and then compressing that archive with gzip. The final compressed file usually has the extension or .
gzip is not to be confused with the archive format, which also uses DEFLATE.
Official source
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