BSArc and BSA

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File Format
Name BSArc and BSA
Extension(s) .bsa, .bs2, .bsn
Released 1991?

.BSA, .BS2, and .BSN are compressed archive formats associated with a group of archiving utilities that includes BSArc (or BS ARChiver) and BSA. They were developed by PhysTechSoft (PTS), a Russian software company better known for the PTS-DOS operating system (Wikipedia article). BSArc is also credited to Serg Babitchew.

BSArc is for DOS. BSA was apparently available for a number of different platforms: It lists DOS, Windows, OS/2, QNX, and Unix.


Format details

The three file extensions seem to correspond to three distinct file formats. But the software name is not always used consistently. Roughly speaking, the "BSArc" software uses .BSA or .BS2 format, and is generally older than the "BSA" software, which (confusingly) uses .BSN format.

It's not just that the software name was changed; there is a BSArc v2.00 (which uses .BS2 format), and a BSA v2.00 (which uses .BSN format).


A possible signature for .BSA format is 0x00 0xAE at offset 1, followed by a byte with value 0x02, 0x03, or 0x07.

.BS2 files probably begin with 0xd4 0x03 'S' 'B' ' ' 0x00.

.BSN files probably begin with signature 0xff 'B' 'S' 'G'. IDArc says this sequence may also start at offset 1 or 3.



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