SCRNCH

SCRNCH is an executable compression utility for DOS. It was developed by Graeme W. McRae, and distributed as shareware.

Discussion
SCRNCH is fundamentally a COM file compressor, but it includes tools and features that make it possible to compress EXE files, by converting them to a COM or COM-like format that SCRNCH can compress, then back to EXE if necessary.

SCRNCH's default COM-to-(COM or EXE) compression mode is called "Run Mode". It also has a mode it calls "Write Mode", which essentially creates self-decompressing files. In the simplest case, Write Mode converts a text file to an executable file that prints the text to the screen. With effort, it can be used for other things, like software installation.

SCRNCH v1.02 supports EXE-format output (but not input) in both modes. V1.00 supports EXE output only in Write Mode.

Identification
(Based on limited testing.)

SCRNCH v1.00-compressed COM files (both modes) start with bytes.

SCRNCH v1.02-compressed COM files, Run Mode, start with.

SCRNCH v1.02-compressed COM files, Write Mode, start with.

SCRNCH v1.02-compressed COM files, both modes, also have at offset 21.

SCRNCH v1.00-compressed EXE files (Write Mode) have at offset 512.

SCRNCH v1.02-compressed EXE files, Run Mode, have at offset 512.

SCRNCH v1.02-compressed EXE files, Write Mode, have at offset 512.

Related formats

 * ZIP - Reportedly[], ZIP's Reduce compression method is based on SCRNCH's compression method.

Software

 * (1988-01-31)
 * (1988-03-28 / 1988-04-04)
 * [ DeSCRE2B] - Utility to help decompress SCRNCHed EXE files