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File Format
Extension(s) .arc
Released 1986

PKARC, later named PKPAK, is an optimized ARC format archiving utility for DOS. It was developed by PKWARE. It is essentially the predecessor of PKZIP.

For information about ARC format, refer to ARC (compression format). This article covers PKARC's extensions, of which there are at least two:

  • The "Squashed" (#9) compression method
  • PK-style comments extension



PKPAK is not to be confused with PAK by NoGate Consulting.


The software began as PKXARC, an extract-only utility. Later, the PKARC compression utility was added. The two utilities were usually distributed together, but had different version numbers until they were synchronized at version 3.5. For the final version, 3.61, PKARC was renamed to PKPAK, and PKXARC to PKUNPAK.

Format details

Compression methods

PKARC introduced one new ARC compression method:

ID Name Description and remarks
9 Squashed LZW, similar to Unix compress. Introduced in PKARC 2.0.

For other ARC compression methods, see ARC (compression format)#Compression methods.

PKARC/PKPAK selects the compression method automatically, and it will often select Squashed unless told not to. Some other ARC utilities have an option to create files that use Squashed compression.

PK-style comments

Archive and file comments use a backward-compatible ARC format extension, in the form of data that appears after the end-of-archive marker. This feature was introduced in PKARC 1.2.

Information based on reverse engineering: An ARC file with PK-style comments ends with an 8-byte trailer that begins with the signature 'P' 'K' 0xaa 0x55. This is preceded by a sequence of 32-byte records, each containing a comment, except for one that has a special purpose. The last 4 bytes of the file contain the offset of the special record. The special record somehow indicates whether an archive comment and/or file comments are present. An archive comment, if present, is in the record preceding the special record. File comment records come after the special record, in the same order as the members appear in the ARC file.

Self-extracting archives

Versions 3.5, 3.6, and 3.61 include a toolkit for making self-extracting ARC archives. It works much like the "MAKESFX" method described in the Self-extracting ZIP article. You're instructed to perform the final step using the DOS "copy" command. It requires an unmodified and correctly-named copy of the original distribution file (PKX35A35.EXE, PK36.EXE, or PK361.EXE).


See also ARC (compression format)#Programs and Utilities.

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