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ARC is a lossless data compression and archival format by (SEA). It was very popular during the early days of networked BBS. The file format and the program were both called ARC. The ARC program essentially made obsolete the use of combinations of the SQ program to compress files and the LU program to create .LBR archives by combining the functions of both compression and archiving into a single program. ARC compresses multiple files into one - but unlike ZIP, not entire directory trees. The .arc format was the subject of quite a bit of controversy in the 1980s - an important event in the open source debate.

.arc is often also used as a file extension for several different file types that have in common that they are some kind of archive files. The Internet Archive uses their own ARC format for storing multiple web resources into a single file [1][2].

In the late 1980s a dispute arose between SEA, maker of the ARC program, and PKWARE (Phil Katz Software). SEA sued Katz for trademark & copyright infringement. The most damning evidence at trial was from an independent software expert appointed by the court to compare the two programs. He stated that PKARC was a derivative work of ARC, pointing out that comments in both programs were often identical and misspelled. Katz settled the lawsuit. This quickly expanded into one of the largest controversies the BBS world ever saw.

The source code for ARC was released by SEA in 1986 and subsequently ported to Unix and the Atari ST in 1987 by Howard Chu. This more portable code base was subsequently ported to other platforms including VAX/VMS and IBM 370 mainframes. Howard's work was also the first to disprove the prevalent belief that Lempel-Ziv encoded files could not be further compressed. Additional compression could be achieved by performing a Huffman Squeeze on the 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.

The ARC format is no longer common on PC desktops but it's still a component in most anti-virus scanners, and as such is still a widely used format, if only behind the scenes.

Filename extension

• .arc (all systems)
• .ark (adopted by some bulletin boards as a naming convention indicating that the file contained software for CP/M rather than MS-DOS).
• .sue (due to all the legal issues)

MIME-Type

• application/octet-stream

See also

• List of archive formats

External links

• ARC - free software Linux/Unix port of the .arc compression program
• nomarch - another free software .arc compression program for Linux/Unix
• The BBS Documentary: Compression - A documentary that discusses ARC history, in the context of BBS
• [3] Specification of an ARC file format used by archive.org