Quantum compression
The Quantum compression format is a little-known data compression method created by David Stafford of Cinematronics, LLC[1]. Rights to it were purchased by Microsoft, and Quantum is one of the possible compression methods in a CAB archive[2]. Quantum uses an extended LZ compression algorithm.
Quantum (.Q) archiver
For DOS, PAQ.EXE is the compressor and UNPAQ.EXE is the decompressor. QWIN.EXE is the Windows decompressor (no Windows compressor is known to exist). It is much faster and has more features (e.g. selective decompression) than the DOS decompressor. Each requires at least a 386 CPU in order to run.
The last known version is 0.97 (as of 15 May, 1995).
.Q archive header
| Bytes | Description |
|---|---|
| 2 | signature, must be 0x44 followed by 0x53 |
| 1 | major version number |
| 1 | minor version number |
| 2 | number of files which reside in this archive |
| 1 | table size required for decompression |
| 1 | compression flags |
This is immediately followed by the list of files:
| Bytes | Description |
|---|---|
| var. | length of file name, see (*) below |
| var. | file name, variable length string, not zero-terminated |
| var. | length of comment field, see (*) below |
| var. | comment field, variable length string, not zero-terminated |
| 4 | fully expanded file size in bytes |
| 2 | file time (DOS format) |
| 2 | file date (DOS format) |
Immediately following the list of files is the compressed data.
(*) Strings are prefixed with their length. This takes one or two bytes. If the length is less than 128 then it is stored directly in one byte. If it is greater than 127 then the high bit of the first byte is set to 1 and the remaining fifteen bits contain the actual length in big-endian format.
References
- ^ http://www.linkedin.com/pub/david-stafford/6/217/576 David Stafford's resumé
- ^ http://www.cabextract.org.uk/ History of CAB files format
- Salomon, David (2007). Data compression: the complete reference. Springer Verlag. p. 187. ISBN 1846286026.
External links
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