compress (Unix)

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File Format
Name compress (Unix)
Ontology
Extension(s) .Z
MIME Type(s) application/x-compress
Wikidata ID Q29209269
Released ~1984
This article is about a specific file format. For compression in general, see Compression.

compress is a Unix command line utility, and a general-purpose compressed file format. Its compression algorithm is based on LZW.

Contents

Identifiers

The conventional filename extension is a capitalized .Z.

Identification

Files begin with bytes 1f 9d.

See also

Formats that could be considered to be the successors of compress include Freeze/Melt, and (especially) Gzip.

The 0x1f compression family

There are several compressed file formats, with similar features, that begin with byte value 0x1f (octal 037; decimal 31). We arbitrarily choose compress as the representative example, and list the formats here.

Signature (hex) Format
1f 1e pack (Unix)
1f 1f pack (Unix) - old format
1f 8b gzip
1f 9d compress
1f 9e Freeze/Melt - old format
1f 9f Freeze/Melt - new format
1f a0 SCO compress LZH
1f a1 Quasijarus Strong Compression
1f ff or ff 1f compact (Unix)

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