compress is a UNIX compression program. It introduces the LZC compression method, which is an LZW implementation which uses variable size pointers as in LZ78.

Description of program

Files compressed by compress are typically given the extension .Z, and most tar programmes will pipes its data through compress when given the command line option -Z.

Files can be returned to their original state using uncompress.

The LZW algorithm that compress is based on was being patented by Sperry Research Center in 1983. The person who applied for the patent published an IEEE article on the algorithm in 1984, 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 (GIF was also implemented this way and later Unisys claimed royalties over it). The patent was granted in 1985 and that 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 of the UNISYS and IBM patents covering the LZW algorithm it makes usage of - 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, 7z, bzip2, gzip, and tar formats.

See also

• Data compression

External links

• Compress for Mac OS X home page

• Source Code for compress v4.0

• ZIP File containing a Windows port of the compress utility