EXEPACK

EXEPACK is an executable compression utility by Microsoft. It compresses DOS EXE files using run-length encoding. It was originally written by Reuben Borman.

It was a part of some development SDKs, and was not a separate product. The compression can be done by the EXEPACK.EXE program, or by a feature integrated into the LINK.EXE program.

There are about a half dozen different versions of the compressed format.

Some of the EXE files included with some versions of MS-DOS were compressed with EXEPACK.

Identification
Apparently, bytes  always appear at offset 16. In other words, the SP field is 128 (refer to MS-DOS EXE).

Bytes  or   appear at offset 20. In other words, the IP field is 16 or 18.

The ASCII signature "" appears immediately preceding the start-of-execution point in the file (refer to MS-DOS EXE).

The characteristic error message "" appears about 200 to 300 bytes after the signature. In rare cases, this message may be translated or erased. D. Fifield suggests searching for the byte sequence that immediately precedes the error message.

Software
Compression:
 * Microsoft's EXEPACK.EXE (or LINK.EXE with /E or /EXEPACK option) - Included with some development SDKs.
 * → Executable Tools Pack → packers/exepack.*
 * Microsoft Macro Assembler v5.1 - Includes EXEPACK 4.06 (on Disk 2)
 * David Fifield's exepack

Decompression, general:
 * unEXEPACK by Samuel Chevet
 * David Fifield's exepack
 * UNEXEPACK from openKB

Decompression, for DOS:
 * See Executable compression for some multi-format utilities that support EXEPACK.
 * by Dan Norstedt. Includes source code.
 * UPACKEXE by Fabrice Bellard - Included with LZEXE.
 * UnPack (archived) by Tenth Planet Software / Clive Turvey

Patchers:
 * by Alan Modra
 * by Steve Burg

Links

 * ModdingWiki: Microsoft EXEPACK
 * Website for David Fifield's exepack
 * EXEPACK and the A20-Gate, from the OS/2 Museum