Editing ARC (file format) (section)

== History ==
In 1985, Thom Henderson of System Enhancement Associates wrote a program called ARC,<ref>{{Cite web|url=http://www.esva.net/~thom/philkatz.html|title=Phil Katz|website=www.esva.net|access-date=15 March 2018}}</ref> based on earlier programs such as [[ar (Unix)|ar]], that not only grouped files into a single archive file but also compressed them to save disk space, a feature of great importance on early personal computers, where space was very limited and modem transmission speeds were very slow. The archive files produced by ARC had file names ending in ".ARC" and were thus sometimes called "arc files".

The source code for ARC was released by SEA in 1986 and subsequently ported to [[Unix]] and  [[Atari ST]] in 1987 by Howard Chu. This more portable [[codebase]] was subsequently ported to other platforms, including [[OpenVMS|VAX/VMS]] and [[IBM System/370]] mainframes. Howard's work was also the first to disprove the prevalent belief that [[LZ77 and LZ78|Lempel-Ziv]] encoded files could not be further compressed. Additional compression could be achieved by using [[Huffman coding]] on the [[Lempel–Ziv–Welch|LZW]] data, and Howard's version of ARC was the first program to demonstrate this property. This hybrid technique was later used in several other compression schemes by [[Phil Katz]] and others.

Later, Phil Katz developed his own shareware utilities, PKARC and PKXARC, to create archive files and extract their contents. These files worked with the archive file format used by ARC and were significantly faster than ARC on the IBM-PC platform due to selective assembly-language coding. Unlike SEA, which combined archive creation and archive file extraction in a single program, Katz divided these functions between two separate utilities, reducing the amount of memory needed to run them. PKARC also allowed the creation of self-extracting archives, which could unpack themselves without requiring an external file extraction utility.

Following the ''System Enhancement Associates, Inc. vs PKWARE Inc. and Phillip W. Katz'' lawsuit, SEA withdrew from the shareware market and developed ARC+Plus.<ref>{{cite magazine
| last        = Vaughan-Nichols
| first       = Steven J.
| date = 1 November 1991
| title=ARC+Plus 7.12. (Software Review) (one of seven evaluations of data compression utility programs in 'Space Savers: Data Compression Utilities') (Evaluation)
| url         = http://www.highbeam.com/doc/1G1-11476636.html
| magazine    = [[Computer Shopper (US magazine)]]
| archive-url=https://web.archive.org/web/20121104024233/http://www.highbeam.com/doc/1G1-11476636.html
| url-status=dead
| archive-date=4 November 2012
| access-date=15 March 2018
}}</ref> This version included a full-screen user interface, with the last known version being 7.12.<ref>{{Cite web|url=http://www.bio.net/bionet/mm/bio-soft/1991-December/002929.html|title=Compression packages (results and site)|website=www.bio.net|access-date=15 March 2018}}</ref> SEA was eventually sold to an unspecified Japanese company in 1992.<ref>{{Cite web|url=http://www.esva.net/thom.html|title=Thom Henderson|website=www.esva.net|access-date=2018-10-16}}</ref>

The ARC format is no longer common on PC desktops, but most [[antivirus software|antivirus]] scanners can still uncompress any ARC archives found in order to detect viruses within the compressed files.