PAK (ARC extension)

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File Format
Name PAK (ARC extension)
Extension(s) .pak, .sdn
Released 1988

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).



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.


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.


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.


Sample files

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