CP Shrink (or CPSHRINK) is a compressed archive program for DOS, and its native .CPZ file format. It was developed by Central Point Software. It usually uses PKWARE DCL Implode compression.
CPSHRINK CPZ archive format overview This information is based on reverse engineering. It may be incorrect or incomplete. Byte order is little-endian. CRC algorithm is CRC-32-IEEE. Sizes and offsets are in bytes, unless otherwise noted. File structure Offset Size Description ------ ---- ----------- 0 8 Archive Header segment 8 32×nmembers Member File Headers segment 8+32×nmembers File Data area Archive Header segment Offset Size Label Description ------ ---- ----- ----------- 0 4 nmembers Number of member files 4 4 CRC of the 32×nmembers bytes following this field Note: The nmembers field might actually be a 2-byte field, followed by 2 bytes of unknown use. Member File Headers segment Sequence of Member File Headers, each 32 bytes, starts at offset 8. Member File Header Offset Size Description ------ ---- ----------- +0 4 CRC of *compressed* file data +4 15 Filename, NUL terminated +19 1 Compression method: 0 = PKWARE DCL Implode, Binary 1 = PKWARE DCL Implode, ASCII 2 = not compressed +20 4 Original size +24 4 Compressed size +28 4 Timestamp (DOS date, time) File Data area The first file's compressed data starts at 8+32×nmembers. Location of other files' data is implied by the sum of the compressed sizes of the preceding files.
There's no quick and easy way to identify a CPZ file from its contents. Validating the CRC of the file headers segment could work, but that segment does not have a fixed size.
- Central Point More PC Tools 2.0 for DOS and Windows (German) → disk1.img → CPSHRINK.EXE (English)
- PC Tools Pro v9.0 (German) → disk1.img → CPSHRINK.EXE (German)
- CP Shrink, from the SAC collection (German)