SCRNCH

Revision as of 19:42, 10 October 2021

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 bb ff ff b4 4a cd 21 81 eb.

SCRNCH v1.02-compressed COM files, Run Mode, start with eb 13 's' 'C' 'e' 'f'.

SCRNCH v1.02-compressed COM files, Write Mode, start with eb 13 's' 'C' 'w' 'f'.

SCRNCH v1.02-compressed COM files, both modes, also have bb ff ff b4 4a cd 21 81 eb at offset 21.

SCRNCH v1.00-compressed EXE files (Write Mode) have bb ff ff b4 4a cd 21 81 eb at offset 512.

SCRNCH v1.02-compressed EXE files, Run Mode, have eb 13 's' 'C' 'h' 'f' at offset 512.

SCRNCH v1.02-compressed EXE files, Write Mode, have eb 13 's' 'C' 'y' 'f' at offset 512.

Related formats

• ZIP - Reportedly[1], ZIP's Reduce compression method is based on SCRNCH's compression method.

Software

• SCRNCH v1.00 (1988-01-31)
• SCRNCH v1.02 (1988-03-28 / 1988-04-04)
• DeSCRE2B - Utility to help decompress SCRNCHed EXE files