Compress
Encyclopedia
Compress is a UNIX
compression program based on the LZC compression method, which is an LZW
implementation using variable size pointers as in LZ78.
.Z. Most tar
programs will pipe their data through compress when given the command line option
Files can be returned to their original state using uncompress
. The usual action of the program is not merely 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).
published an IEEE article on the algorithm in 1984, but failed to note that he had applied for a patent on the algorithm. Spencer Thomas took this article and implemented compress in 1984, without realizing that a patent was pending on the LZW algorithm. The GIF image format also incorporated LZW compression in this way, and Unisys
later claimed royalties on implementations of GIF. Joseph M. Orost led the team and worked with Thomas 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. was granted in 1985, and this is why compress could not be used without paying royalties to Sperry Research, which was eventually merged into Unisys. compress has fallen out of favor in particular user-groups because it makes use of the LZW algorithm, which was covered by a Unisys patent — 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 US LZW patent expired in 2003, so it is now in the public domain in the United States. All patents on the LZW worldwide have also expired (see Graphics Interchange Format#Unisys and LZW patent enforcement).
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
compression program based on the LZC compression method, which is an LZW
LZW
Lempel–Ziv–Welch is a universal lossless data compression algorithm created by Abraham Lempel, Jacob Ziv, and Terry Welch. It was published by Welch in 1984 as an improved implementation of the LZ78 algorithm published by Lempel and Ziv in 1978...
implementation using variable size pointers as in LZ78.
Description of program
Files compressed by compress are typically given the extensionFilename extension
A filename extension is a suffix to the name of a computer file applied to indicate the encoding of its contents or usage....
.Z. Most tar
Tar (file format)
In computing, tar is both a file format and the name of a program used to handle such files...
programs will pipe their data through compress when given the command line option
-Z (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
Uncompress
uncompress is a shell command in Unix-like environments.The uncompress utility will restore files to their original state after they have been compressed using the compress utility. If no files are specified, the standard input will be uncompressed to the standard output.This utility supports...
. The usual action of the program is not merely 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).
History
The LZW algorithm used in compress was patented by Sperry Research Center in 1983. Terry WelchTerry Welch
Terry A. Welch is an American computer scientist. Along with Abraham Lempel and Jacob Ziv, he developed the lossless LZW compression algorithm which was published in 1984.Welch received a B.S., M.S. and Ph.D. degree at MIT in electrical engineering...
published an IEEE article on the algorithm in 1984, but failed to note that he had applied for a patent on the algorithm. Spencer Thomas took this article and implemented compress in 1984, without realizing that a patent was pending on the LZW algorithm. The GIF image format also incorporated LZW compression in this way, and Unisys
Unisys
Unisys Corporation , headquartered in Blue Bell, Pennsylvania, United States, and incorporated in Delaware, is a long established business whose core products now involves computing and networking.-History:...
later claimed royalties on implementations of GIF. Joseph M. Orost led the team and worked with Thomas et al. to create the 'final' (4.0) version of compress and published it as free software to the 'comp.sources.unix' USENET
Usenet
Usenet is a worldwide distributed Internet discussion system. It developed from the general purpose UUCP architecture of the same name.Duke University graduate students Tom Truscott and Jim Ellis conceived the idea in 1979 and it was established in 1980...
group in 1985. was granted in 1985, and this is why compress could not be used without paying royalties to Sperry Research, which was eventually merged into Unisys. compress has fallen out of favor in particular user-groups because it makes use of the LZW algorithm, which was covered by a Unisys patent — because of this, gzip
Gzip
Gzip is any of several software applications used for file compression and decompression. The term usually refers to the GNU Project's implementation, "gzip" standing for GNU zip. It is based on the DEFLATE algorithm, which is a combination of Lempel-Ziv and Huffman coding...
and bzip2
Bzip2
bzip2 is a free and open source implementation of the Burrows–Wheeler algorithm. It is developed and maintained by Julian Seward. Seward made the first public release of bzip2, version 0.15, in July 1996.-Compression efficiency:...
increased in popularity on Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
-based operating systems due to their alternative algorithms. compress has, however, maintained a presence on Unix
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
and BSD systems. The US LZW patent expired in 2003, so it is now in the public domain in the United States. All patents on the LZW worldwide have also expired (see Graphics Interchange Format#Unisys and LZW patent enforcement).
External links
- ncompress - public domain compress/uncompress implementation for POSIX systems
- compress - original Unix compress (in a compress'd archive)
- compress - original Unix compress executable (gzip'd)
- Source Code for compress v4.0 (gzip'd sharchive)
- ZIP File containing a Windows port of the compress utility
- source code to the current version of fcompress.c from compress