DWC

Revision as of 13:24, 19 October 2023

DWC is a compressed archive utility and file format that was patterned after ARC, but is not compatible with that format. It was designed to be faster and more compact than ARC, but have similar functionality. Its compression scheme is based on LZW.

It includes a utility to make self-extracting archives.

Discussion

DWC was created by Dean W. Cooper in 1986 as a higher performance alternative to the ARC (both ARC & PKARC) and Zoo file archiving tools. The file COMPARE.DOC (in e.g. version A5.01) reports both compression and time improvements over DWC's competitors.

Source code for some versions prior to A5.01 was apparently made public, but we have not located any copies.

The documentation says that in 1988 the compressor/decompressor source code rights were sold to a company called DS Technologies.

File structure

DWC archive format overview

 This documentation contains educated guesswork derived from
  observing the behavior of DWC (mainly v5.10). It extends and
  corrects some earlier descriptions of the format.

 - Byte order is little-endian.
 - CRC algorithm is CRC-16/ARC.
 - Sizes and offsets are in bytes, unless otherwise noted.

Archive Trailer segment

 Let EOF = the DWC file size.

 Offset   Size Label     Description
 ------   ---- -----     -----------
 EOF-27   2    tsize     Size of trailer (usually 27, larger OK)
 EOF-25   1    fhsize    Size of each member file header (usually 34,
                          larger OK, slightly smaller maybe OK)
 EOF-24   13             Name of header file ("h" command), NUL-
                          terminated
 EOF-11   4              Archive timestamp (Unix time)
 EOF-7    4    nmembers  Number of member files
 EOF-3    3              "DWC" signature

Member File Headers segment

 Sequence of nmembers headers, each fhsize bytes, starts at
 EOF-tsize-(fhsize×nmembers).

Member File Header

 Offset   Size Label     Description
 ------   ---- -----     -----------
 +0       13             Base filename, NUL terminated
 +13      4              Original size
 +17      4              Timestamp (Unix time)
 +21      4    csize     Compressed size
 +25      4    fdpos     Offset (from start of file) of File Data segment
 +29      1              Low 4 bits: Compression method (1=Crunched,
                          2=not compressed).
                         0x40 bit: Set if file is encrypted.
 +30      1    cmtsize   Size of comment field
 +31      1    pathsize  Size of path field
 +32      2              CRC of *compressed* (and potentially encrypted)
                          data

File Data

 One segment per member file. Starts at fdpos.

 Offset           Size      Description
 ------           ----      -----------
 +0               csize     Compressed data
 +csize           pathsize  Path, NUL-terminated
 +csize+pathsize  cmtsize   File comment, NUL-terminated

Identification

Files end with ASCII "DWC". There is no header or signature at the beginning of the file.

The known versions of DWC always seem to produce files having bytes 1b 00 22 beginning 27 bytes from the end of the file. However, the software does not require this, and old versions still need to be evaluated.

Specifications

• Archive format info, including DWC
• DWC format info, from Corion.net and FileFormat.Info

Software

• DWC (DOS binaries)
  • Ver. A4.95 (1988-03-15)
  • Ver. A5.01 (1988-05-31)
  • Ver. A5.10 (1990-03-07)