PAK (ARC extension)
PAK is a DOS utility for managing compressed archive files, developed by NoGate Consulting. It is also the name of one of the file formats it supports: .PAK format.
PAK format is an extension of ARC format. The differences are that it may use some PAK-specific compression methods (see below), and that it has some features made possible by "extended records" stored after the end-of-archive marker.
PAK was originally named GSARC (and used filename extension .ARC), but was quickly renamed to PAK (and the default extension changed to .PAK).
See ARC for more information relevant to PAK format. See also SDN (SDN Project).
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Disambiguation
See PAK for more formats named PAK.
Format details
Compression methods
ARC compression methods unique to PAK:
| ID | Name | Description and remarks |
|---|---|---|
| 10 | Crushed | RLE90 + LZW (or LZMW?) |
| 11 | Distilled | LZ77 + static Huffman coding. Introduced in PAK v2.0. |
For other ARC compression methods, see ARC (compression format)#Compression methods.
Self-extracting archives
All versions of PAK and GSARC can create self-extracting EXE archives, either with the /EXE option, or the included EXEMAKE.EXE utility. The original distribution files (e.g. PAK251.EXE) use this format.
Such archives contain an embedded PAK file, with apparently one special case: PAK v1.6 (and only that version) when the file includes remarks (comments). In that case, the remarks are interleaved with the member files in a way that is not normal for PAK format.
Identification
PAK format files made by PAK/GSARC v1.0 typically start with bytes 0x1a 0x0a, and end with 0x1a 0x00.
Files made by PAK v1.5–1.6 typically start with 0x1a 0x0a, and end with 0xfe 0x00.
Files made by PAK v2.0+ typically start with 0x1a 0x0b, and end with 0xfe 0x00.
A file that ends with 0xfe 0x00 could also be identifiable as PAK format if the first byte is 0x1a and the second is 0x02, 0x08, or 0x09. That could happen if the first member file was not compressible, or was compressed with non-default options.
Identification of self-extracting archives
Self-extracting archives for a given version are highly formulaic, and should be easy to identify as such. But it's not clear that there's any simple way to identify all versions.
For GSARC and PAK v1.0, the byte sequence
fb ba 53 03 2e 89 16 65 01 b4 30 cd 21 8b 2e 02
appears at offset 512.
The byte sequence
55 8b ec 8b 46 0a 8b 4e 08 0b c9 74 17 c4 76 04
appears at offset 512 for v1.51-1.6, offset 513 for v2.01-2.10, or offset 515 for v2.50-2.51.
Specifications
The PAK.DOC file contained in the v2.51 distribution includes basic information about .PAK/.ARC format, including the extended records. It does not document the compression schemes in detail.
Software
- GSARC v1.0 (1988-10-13) (DOS binary)
- PAK (DOS binaries)
- v1.0 (1988-10-17)
- v1.51 (1989-01-15)
- v1.6 (1989-01-24)
- v2.01 (1989-07-31): Magnum One → D2/PAK201.EXE
- v2.10 (1989-08-10)
- v2.50 (1990-09-20)
- v2.51 (1990-10-08)
- Another copy, packaged differently
- Various versions at old-dos.ru
- PAKF - A menu-driven edition of PAK (commercial software)
- The Unarchiver - Supports the PAK-specific compression schemes
- Deark - Can decompress method 11, but probably not 10.
Sample files
- ARC2PAK1.PAK (compression method 10)
- IE111SEP.ZIP → INTRECHO.PAK (compression method 11)
Self-extracting archives:
- TDESIGN.ZIP → *.EXE (v1.0)
- CSS30.ZIP → SCREENS.EXE (v1.6), PROGRAM.EXE (~v2.51)
- PACE.ZIP → *.EXE (~v2.10)
- asa57.zip → ASA57U.EXE (~v2.51)
