ArcMac

ArcMac format is a variant of the ARC compressed archive format, with extended features relevant to classic Macintosh computers. It is associated with the ArcMac software by Don Gilbert and dogStar Software.

Discussion
There are three applications:
 * ArcMac - The full software for Mac (shareware)
 * ArcPop - Decompression-only software for Mac
 * xArcMac - Decompression-only software for DOS

Some "ArcMac" or "ArcPop" distributions don't contain all three.

The version numbers and release dates of these things, and of the included documentation, do not seem to have been updated consistently, and are difficult to make sense of.

The documentation claims that the distribution includes source code for ArcPop and xArcMac, in a file named "MARCS.ARC". Unfortunately, we have not located such a file.

Identification
ArcMac files start with, and have at offset 59, as the start of an ARC-compatible header.

Specifications

 * Refer to the "ArcMac File Structure" section in the ArcMac2.Doc or ARCMAC.DOC file included with most ArcMac distributions.
 * macutil → macunpack/arc.h has some info (though macunpack does not support the format)

Software

 * xArcMac v1.1a
 * - ArcMac v1.2a? (MacBinary-encoded (self-extracting?) ArcMac file)
 * Macintosh Repository: "ArcMac"
 * Macintosh Garden: "ArcMac v1.3"
 * Mac GUI: "ArcPop 1.2a"
 * Mac GUI: "ArcMac v1.2a"
 * Mac GUI: "ArcMac"
 * Mac GUI: "Arcmac1.3e"
 * Mac GUI: "Arcpop"

The extent to which ArcMac format is compatible with ARC decompressors that are not ArcMac-aware is unclear. It can work in some limited cases, but is not reliable.