Microsoft SZ installation compression

File Format
Name	Microsoft SZ installation compression
Ontology	Electronic File Formats Compression Microsoft SZ installation compression
Extension(s)	.??$
Wikidata ID	Q105851650
Released	≤1990

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 53 5a 20 88 f0 27 33. This is normally followed by d1, 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)
• ANORMAL's DOSEXE collections → Compiler pack → microsoft/quickbasic-4.50.rar → quickbasic-4.50/1400k disks/UNPACK.EXE - "Microsoft BASIC Unpack Utility - Version 1.10" (decompression only)
• libmspack

Sample files

• Examples of SZ files may be found in packages containing a decompression utility; see the Software section.
• WinWorld: MS-DOS 5.0 → "Microsoft MS-DOS 5.00 (Beta 5.0.224)" → ... → *.??$