BSArc and BSA

.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).

Identification
A possible signature for .BSA format is at offset 1, followed by a byte with value, , or.

.BS2 files probably begin with.

.BSN files probably begin with signature. IDArc says this sequence may also start at offset 1 or 3.

Software

 * BSArc at old-dos.ru
 * BSA at old-dos.ru
 * BSArc V1.9.3 (DOS software, Russian)
 * BSA 2.00 Rel 0.972 (DOS software, English)
 * BSA 2.0 Rel 1.10 (DOS software, English)

Links

 * PhysTechSoft website