SCRNCH

File Format
Name	SCRNCH
Ontology	Electronic File Formats Compression Executable compression SCRNCH
Released	1988

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