Gzip
Encyclopedia : G : GZ : GZI : Gzip
- The correct title of this } is }}}. The initial letter is capitalized due to [Naming conventions #Lower case first lettertechnical restrictions].
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
gzip is not to be confused with the ZIP archive format, which also uses DEFLATE. The ZIP format is more portable and can hold collections of files without resorting to 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.
Other uses
The HTTP/1.1 protocol allows for clients to optionally request the compression of content from the server. The standard itself specifies two compression methods: "gzip" (the content wrapped in a gzip stream) and "deflate" (the content in a raw, headerless DEFLATE stream). Both are supported by many HTTP client libraries and almost all modern browsers.Since the late 1990s, bzip2, a file compression utility based on a block-sorting algorithm, has gained some popularity as a gzip replacement. It produces considerably smaller files (especially for source code and other structured text), but at the cost of memory and processing time (up to a factor of 4). bzip2-compressed tarballs are conventionally named .tar.bz2.
AdvanceCOMP has a DEFLATE implementation which produces gzip-compatible files with better compression ratios than gzip itself.
The corresponding program for unzipping programs zipped with gzip is gunzip.
See also
- redirect
- List of archive formats
- List of file archivers
- Comparison of file archivers
- List of Unix programs
- .tar.gz.gpg
- Free file format
External links
- gzip [file format specification]
- [gzip Home Page] and http://www.gzip.org/
- [Zlib Home Page]
- [List of GZIP related resources, tutorials, sources]
- [The gzip Recovery Toolkit]
- [The Online Marketing Benefits of gzip]
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.