OS/2 PACK2 archive

File Format
Name	OS/2 PACK2 archive
Ontology	Electronic File Formats Archiving OS/2 PACK2 archive
Extension(s)	.??_, .??@, others

OS/2 PACK2 archive (maybe also called FTCOMP format) is a compressed archive format used on OS/2, particularly by software installers.

See also OS/2 PACK archive.

Discussion

On the OS/2 3.0 and 4.0 installation disks, some PACK2 files are named with a trailing underscore, like "DSPRES.DL_". These archives contain a single compressed file, and are named after that file with the last letter replaced with an underscore. Some PACK2 files are named with no extension, like "BUNDLE" or "KLONDIKE" or "SERIAL". These archives contain a collection of compressed files - "BUNDLE" if there's no other archive in the same directory, or some name specific to its contents.

PACK2 format is associated with the PACK2.EXE and UNPACK2.EXE utilities. In some cases, the "UNPACK" command can decompress PACK2 format, but this apparently works by using the UNPACK2.EXE utility behind the scenes.

Format details

Shortly after the filename of each member file is what might be a FourCC code for the compression method or format version. Two codes are known to exist: "fT19", and, much more rarely, "fT21".

Identification

Files begin with bytes a5 96 fd ff. ASCII "FTCOMP" appears at offset 24.

Compare to OS/2 PACK archive#Identification.

Software

• The OS/2 3.0 and 4.0 install CDs contain OS/2 command-line tools UNPACK.EXE and UNPACK2.EXE (some files that cannot be unpacked with UNPACK will work with UNPACK2)
• The OS/2 Developer's Toolkit contains OS/2 command-line tools PACK.EXE and PACK2.EXE
• WinWorld: PC-DOS 7.x → "IBM PC-DOS 7.0 (3.5-XDF)" → 144US1.DSK → UNPACK2.EXE (for DOS)
• https://github.com/martinlindhe/formats (Maybe just parses the header.)

Caution: Some PACK2 archives contain absolute file paths, which by default are respected by some or all UNPACK utilities.

Sample files

• http://cd.textfiles.com/venus/64v2/os2/ → *.pk2
• http://cd.textfiles.com/hobbesos29709/disk1/GAMES/MAH21DE.ZIP → *@
• http://cd.textfiles.com/hobbesos29709/disk1/GAMES/SEAHAV23.ZIP → *_
• http://cd.textfiles.com/hobbesos29709/disk1/GAMES/TOYLAND.ZIP → *_
• WinWorld: PC-DOS 7.x → "IBM PC-DOS 7.0 (3.5-XDF)" → 144US2.XDF → BACKUP1, etc. ("fT21" format)
• dexvert samples — archive/os2FTCOMP