LZWCOM - Revision history

Jsummers: /* Software */

2023-03-01T17:49:21Z

‎Software

Jsummers at 18:23, 25 February 2021

2021-02-25T18:23:31Z

Jsummers: Created page with "{{FormatInfo |formattype=electronic |subcat=Compression |released=~1985 }} '''LZWCOM''' is a file compression utility, and associated file format, developed by Kent Williams. ..."

2021-02-25T18:14:09Z

Created page with "{{FormatInfo |formattype=electronic |subcat=Compression |released=~1985 }} '''LZWCOM''' is a file compression utility, and associated file format, developed by Kent Williams. ..."

New page

{{FormatInfo
|formattype=electronic
|subcat=Compression
|released=~1985
}}
'''LZWCOM''' is a file compression utility, and associated file format, developed by Kent Williams. It uses hashed [[LZW]] compression. The companion decompression utility is '''LZWUNC'''.

== Format details ==
The format was changed in an incompatible way in v2.0, to insert a [[CRC-16]] field (apparently [[CRC-16#CRC-16/ARC|CRC-16/ARC]]) after every 1024 bytes of compressed data. It is a CRC of the ''compressed'' data, not the decompressed data.

== Identifiers ==
The software does not have a default filename extension or naming pattern. It's not clear if any conventions emerged.

== Identification ==
LZWCOM format has no header or signature. If a file is at least 1026 bytes in size, then the CRC field at offset 1024 (and 2050, 3076, ...) can be tested to identify v2 format with decent accuracy. Other than that, there's probably no good way to identify an LZWCOM file from its contents.

== Related formats ==
LZWCOM's compression scheme was used, sometimes with minor changes, by:
* [[ARC (compression format)|ARC]] - compression methods 5 and 6
* [[Crunch]] - especially Crunch v1.x format
* [[ZSQ (LZW compression)|ZSQ]]

== Software ==
There appear to be at least three releases of the software. Two of them lack a version number; we'll call them "first release" and "second release".

* LZWCOM/LZWUNC
** First release (unknown date). Reported to be buggy.
*** [http://cpmarchives.classiccmp.org/cpm/mirrors/oak.oakland.edu/pub/cpm/squsq/lzw.lbr lzw.lbr] - Source code and CP/M binaries
** Second release (≤1985-03-11)
*** [https://archive.org/details/cdrom-wc-cdrom-cusersgrouplibrary-1994-08 Walnut Creek CD-ROM - The C Users' Group Library - August 1994] → VOL_100/181_01/... - Source code, DOS binaries, etc. (What a mess. The relevant files are READ_ME, DEBUG.H, and the *LZW* files, except LZW.C which is from an older version.)
** Version 2.0 (≤1985-08-20)
*** {{CdTextfiles|carousel344/026/LZW.ZIP|LZW.ZIP}} - DOS binaries and (incomplete?) source code

== Links ==
* [https://archive.org/details/The_Boston_Kugel_1988_May-June_Volume_5_Number_2/page/n2/mode/1up A Whirlwind Look at the World of File Compression] - Article in The Boston Kugel, May-June 1998, p. 3
* [https://archive.org/download/cdrom-wc-cdrom-cusersgrouplibrary-1994-08/wc-cdrom-cusersgrouplibrary-1994-08.iso/VOL_100%2F181_01%2FREAD_ME READ_ME] - Some messages about the software

@@ Line 31: / Line 31: @@
 ** Version 2.0 (≤1985-08-20)
 *** {{CdTextfiles|carousel344/026/LZW.ZIP|LZW.ZIP}} - DOS binaries and (incomplete?) source code
 == Links ==
 * [https://archive.org/details/The_Boston_Kugel_1988_May-June_Volume_5_Number_2/page/n2/mode/1up A Whirlwind Look at the World of File Compression] - Article in The Boston Kugel, May-June 1988, p. 3
 * [https://archive.org/download/cdrom-wc-cdrom-cusersgrouplibrary-1994-08/wc-cdrom-cusersgrouplibrary-1994-08.iso/VOL_100%2F181_01%2FREAD_ME READ_ME] - Some messages about the software

@@ Line 7: / Line 7: @@
 == Format details ==
-The format was changed in an incompatible way in v2.0, to insert a [[CRC-16]] field (apparently [[CRC-16#CRC-16/ARC|CRC-16/ARC]]) after every 1024 bytes of compressed data. It is a CRC of the ''compressed'' data, not the decompressed data.
+Version 2.0 of the software changed the format in an incompatible way. It inserts a [[CRC-16]] field (apparently [[CRC-16#CRC-16/ARC|CRC-16/ARC]]) after every 1024 bytes of compressed data. It is a CRC of the ''compressed'' data, not the decompressed data.
 == Identifiers ==
@@ Line 33: / Line 33: @@
 == Links ==
-* [https://archive.org/details/The_Boston_Kugel_1988_May-June_Volume_5_Number_2/page/n2/mode/1up A Whirlwind Look at the World of File Compression] - Article in The Boston Kugel, May-June 1998, p. 3
+* [https://archive.org/details/The_Boston_Kugel_1988_May-June_Volume_5_Number_2/page/n2/mode/1up A Whirlwind Look at the World of File Compression] - Article in The Boston Kugel, May-June 1988, p. 3
 * [https://archive.org/download/cdrom-wc-cdrom-cusersgrouplibrary-1994-08/wc-cdrom-cusersgrouplibrary-1994-08.iso/VOL_100%2F181_01%2FREAD_ME READ_ME] - Some messages about the software