SOF (Spectrum Software)
SOF is a compressed archive format, associated with software by Spectrum Software (of Des Moines, Iowa?).
The compression utility is named RESOF, and the decompression utility is DESOF. The format doesn't seem to have an official name, and is sometimes known as "RESOF" format.
This article is based on version "2.0 Beta" of the software, the only one that has been found. Its behavior implies the existence of an older SOF format that was quite different.
Format details
SOF is a slightly modified variant of ZIP.
Known differences from ZIP:
- In the "end of central directory" record, the "size of central directory" field is a signed 32-bit integer whose value is the negative of what it would be in ZIP.
- The
'P' 'K' 0x01 0x02signature is instead'P' 'K' 0x01 0x04. - The
'P' 'K' 0x03 0x04signature is instead'P' 'K' 0x03 0x06.
RESOF has only been observed to use ZIP compression methods 1 (Shrink) and 0 (Stored).
DESOF possibly also supports methods 2-5 (Reduce) and 6 (Implode).
Identification
SOF files presumably always start with bytes 'P' 'K' 0x03 0x06, and (like most ZIP files) have bytes 'P' 'K' 0x05 0x06 beginning 22 bytes from the end of the file.
