.arc
| Filename extension | .arc, .ark, .sue |
|---|---|
| Internet media type | application/octet-stream |
| Uniform Type Identifier (UTI) | public.archive.arc |
| Developed by | System Enhancement Associates |
| Type of format | Data compression |
ARC is a lossless data compression and archival format by System Enhancement Associates (SEA). The file format and the program were both called ARC. The format is perhaps best known as the subject of controversy in the 1980s, part of important debates over what would later be known as open formats.
ARC was extremely popular during the early days of the dial-up BBS. ARC was convenient as it combined the functions of the SQ program to compress files and the LU program to create .LBR archives of multiple files. The format was later replaced by the ZIP format, which offered better compression ratios and the ability to retain directory structures through the compression/decompression process.
The .arc file extension is often used for several file archive-like file types. For example, the Internet Archive uses its own ARC format to store multiple web resources into a single file. The FreeArc archiver also uses .arc extension, but uses a completely different file format. Nintendo uses an unrelated 'ARC' format for resources, such as MIDI, voice samples, or text, in GameCube and Wii games. Several unofficial extractors exist for this type of ARC file.
In 1985, Thom Henderson of System Enhancement Associates wrote a program called ARC, based on earlier programs such as 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 sometimes called "arc files" as a result.
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 System/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 using Huffman coding 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.
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