PAQ

File Format
Name	PAQ
Ontology	Electronic File Formats Archiving PAQ
Extension(s)	.pa6, .pa7, .pa8, .paq8p, others
Released	2002

For other "PAQ" formats, see oPAQue, PAQJ, and Quantum compressed archive.

PAQ is actually a whole series of different compression programs and their associated file formats, designed to achieve maximum compression (for which the various versions have won some awards) at the possible expense of being slow and taking a lot of memory. Since compatibility (either forward or backward) among the different PAQ versions was not preserved, there are a wide assortment of incompatible formats associated with this group of programs, with new versions devised to implement improved compression techniques or techniques carefully tailored for particular sorts of data without regard for retaining the ability to compress or decompress the files created by earlier versions.

Since PAQ is open-source, there have been "forks" producing yet more adapted and incompatible versions.

The author of PAQ (Matt Mahoney) also created BARF as a sort of reducio ad absurdum of file compression techniques.

Identification

• PAQ1, PAQ2, PAQ3, PAQ4 and PAQ5 files start with ASCII PAQ, followed by ASCII 1 to 5 respectively, followed by a Windows line break (bytes 0x0d 0x0a = CRLF = \r\n).
• PAQ6 files start with ASCII PAQ6 -, followed most likely by ASCII 0 to 9 for the chosen memory consumption model, followed by a Windows line break (bytes 0x0d 0x0a = CRLF = \r\n).
• PAQ7 files start with ASCII paq7 -, followed most likely by ASCII 1 to 5 for the chosen memory consumption model, followed by a Windows line break (bytes 0x0d 0x0a = CRLF = \r\n).

See also

• ZPAQ

References

• Wikipedia article
• Official site