Microsoft SZ installation compression

Microsoft SZ installation compression refers to a compressed file format that was used by some Microsoft software distributions.

It is presumably an early version of the MS-DOS installation compression formats. The libmspack documentation calls it the "QBasic variant".

Discussion
One of the SZ utilities calls itself "lzw 1 Compression Utility". However, the format does not use LZW compression. It uses Okumura's LZSS.

Identification
Files start with bytes. This is normally followed by, but other values are used by the file splitting feature, for fragments after the first one.

Specifications

 * libmspack: COMPRESS.EXE file formats

Software

 * Dr. Windows 3 → dr win3/DATABASE/ACCSDBS.ZIP → COMPRESS.EXE - "A lzw 1 Compression Utility - Version 1.00" (compression and decompression)
 * → Compiler pack → microsoft/quickbasic-4.50.rar → quickbasic-4.50/1400k disks/UNPACK.EXE - "Microsoft BASIC Unpack Utility - Version 1.10" (decompression only)
 * libmspack
 * libmspack

Sample files

 * Examples of SZ files may be found in packages containing a decompression utility; see the Software section.