PKARC/PKPAK
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
Contents |
Disambiguation
PKPAK is not to be confused with PAK by NoGate Consulting.
Discussion
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).
Software
Let Grab Bag = Shareware Grab Bag → Shareware_Grab_Bag_1988.zip.
- PKXARC 1.1 (1985-10-21): PKArc at old-dos.ru → PKxArc 1.1
- PKXARC 2.3 (1986-02-11): Grab Bag → 014/pkxarc23.arc
- PKXARC 2.4 (no copy found)
- PKXARC 2.5 (no copy found)
- PKXARC 2.6 (1986-03-22): Grab Bag → 014/pkxarc26.arc
- PKXARC 2.7 (no copy found)
- PKXARC 3.0 (1986-04-05): Grab Bag → 014/pkxarc30.arc
- PKXARC 3.1 (no copy found)
- PKXARC 3.2 (no copy found)
- PKARC 1.0 (1986-08-06) (no copy found)
- PKARC 1.1 (1986-09-12) (no copy found)
- PKARC 1.2 + PKXARC 3.3 (1986-10-23): Grab Bag → 014/pkx33a12.com
- PKARC 2.0 + PKXARC 3.4 (1986-12-15): Grab Bag → 014/pkx34a20.com
- PKARC/PKXARC 3.5 (1987-04-27): Grab Bag → 011/pkx35a35.exe
- PKARC/PKXARC 3.6 (1988-06-01)
- PKPAK/PKUNPAK 3.61 (1988-08-02)
- Various versions at old-dos.ru: PKXARC/PKARC, PKPAK
- SQUASH.ZIP - Public domain decompression code for the "Squashed" method
