gzip is a software application used for file compression. gzip is short for GNU zip; the program is a free software replacement for the compress program used in early Unix systems, intended for use by the GNU Project.

gzip was created by Jean-Loup Gailly and Mark Adler. Version 0.1 was first publicly released on October 31, 1992. Version 1.0 followed in February 1993.

OpenBSD's version of gzip is actually the compress program, to which support for the gzip format was added in OpenBSD 3.4 - the 'g' here stands for gratis.1

File format
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, a version number and a timestamp
optional extra headers, such as the original file name,
a body, containing a DEFLATE-compressed payload
an 8-byte footer, containing a CRC-32 checksum and the length of the original uncompressed data
Although its file format also allows for multiple such streams to be concatenated together (these are simply decompressed concatenated as if they were one), gzip is normally used to compress just single files. Compressed archives are typically created by assembling collections of files into a single tar archive, and then compressing that archive with gzip. The final .tar.gz or .tgz file is usually called a tarball.

gzip is not to be confused with the ZIP archive format, which also uses DEFLATE. The ZIP format can hold collections of files without an external archiver, but is less compact than compressed tarballs holding the same data because it compresses files individually and cannot take advantage of redundancy between files (solid compression).

zlib is an abstraction of the DEFLATE algorithm in library form which includes support both for the gzip file format and a lightweight stream format in its API. The zlib stream format, DEFLATE and the gzip file format were standardized respectively as RFC 1950, RFC 1951 and RFC 1952.

The corresponding program for uncompressing gzipped files is gunzip. Both commands call the same binary; gunzip has the same effect as gzip -d.

from wikipedia

Last edited Jul 1, 2008 at 11:31 AM by okaninecikli, version 2