Compress 205779 199855676 2008-03-21T16:42:53Z Jengelh 287849 misc typography {{lowercase|title=compress}} {{This|the data compression utility|Compression}} '''compress''' is a [[Unix|UNIX]] compression program based on the ''LZC'' compression method, which is an [[LZW]] implementation using variable size pointers as in [[LZ78]]. == Description of program == Files compressed by ''compress'' are typically given the [[filename extension|extension]] '''.Z'''. Most [[tar (file format)|tar]] programs will [[pipe (Unix)|pipe]] their data through ''compress'' when given the command line option <code>'''-Z'''</code> (tar in itself does not compress, it just stores multiple files within one tape archive file). Files can be returned to their original state using [[uncompress]]. The usual action of the program is not to create an uncompressed copy of the file, but to uncompress the compressed file (so that the uncompressed version retains the timestamp and other attributes of the compressed file). The LZW algorithm used in ''compress'' was patented by Sperry Research Center in 1983. The person who applied for the patent published an IEEE article on the algorithm in 1984<ref>Welch, Terry A., "A technique for high performance data compression", IEEE Computer, 17(6), pp.8-19, June 1984.</ref>, without mentioning that the algorithm was patent pending. Spencer Thomas took this article and implemented ''compress'' in 1984, without realizing that the LZW algorithm was patent pending. (The [[Graphics Interchange Format|GIF]] image format also incorporated LZW compression in this way and later [[Unisys]] claimed royalties on implementations of GIF.) Joseph M. Orost led the team and worked with Spencer et al. to create the 'final' (4.0) version of ''compress'' and published it as free software to the 'comp.sources.unix' [[USENET]] group in 1985. The patent on LZW compression was granted in 1985 and this is why ''compress'' could not be used without paying royalties to Sperry Research (which became Unisys). ''compress'' has fallen out of favor in particular user-groups because it makes use of the LZW algorithm, which is covered by UNISYS and IBM patents — because of this, [[gzip]] and [[bzip2]] increased in popularity on [[Linux]]-based operating systems due to their alternative algorithms. ''compress'' has however maintained a presence on [[Unix]] and [[BSD]] systems. The LZW patent expired in 2003, so it is now in the public domain in the United States. == 'compress' for Mac OS X == There is also a [[Freeware]] [[Mac OS X]] application with the same name; but it is completely unrelated with the former. This program supports the [[ZIP (file format)|zip]], [[7z]], [[bzip2]], [[gzip]], and tar formats. A much earlier program dating from the 1980s, '''MacCompress''', is a [[Mac OS]] [[GUI]] wrapper for compress, but has not been used for some time. The [[Darwin (operating system)|Darwin operating system]] includes a compress utility as described above, accessed from A Drive. == See also == * [[Data compression]] * [[Image compression]] * [[List of Unix programs]] == External links == * [http://ncompress.sourceforge.net/ ncompress] - public domain compress/uncompress implementation for POSIX systems * [http://www.fromconcentratesoftware.com/Compress/ Compress for Mac OS X home page] * [http://ibiblio.org/pub/linux/utils/compress/compress.tar.Z compress] - original Unix compress (in a compress'd archive) * [http://ibiblio.org/pub/linux/utils/compress/compress.z compress] - original Unix compress executable (gzip'd) * [ftp://ftp.uu.net/systems/unix/bsd-sources/usr.bin/compress/ Source Code for compress v4.0] * [http://www.willus.com/archive/unixcmds.zip ZIP File containing a Windows port of the compress utility] == References == <references/> {{Compression Software Implementations}} [[Category:Data compression software]] [[Category:Unix software]] [[de:compress]] [[fr:compress]] [[ja:UNIX Compress]] [[ko:유닉스 compress]]