What is Z?

Z files use Unix compress utility - LZW (Lempel-Ziv-Welch) compression algorithm. Created by Spencer W. Thomas at University of California (1985). First widely-used Unix compression tool (pre-gzip). Command: compress file → file.Z, uncompress file.Z → file. Simple, fast compression but lower ratio than modern alternatives. Common in 1980s-1990s Unix systems (SunOS, HP-UX, AIX). File extension: .Z (uppercase, distinguishes from .tar.gz). Often combined with tar: .tar.Z archives (Unix software distribution).

Z format is largely obsolete - gzip (1992) replaced compress with better compression and no patent issues. LZW patent (expired 2003) hindered compress adoption. Historical context: Unix systems standardized on compress before gzip existed. Legacy content: old Unix backups, archived software tarballs, vintage systems. Modern tools: gzip can decompress .Z files (gunzip file.Z), 7-Zip supports .Z, compress utility still available on some Unix systems. Replaced by: gzip (.gz, better ratio), bzip2 (.bz2, higher compression), XZ (.xz, modern standard).

Did you know? compress was the standard Unix compression before gzip - pioneered CLI compression!

History

Unix compress introduced LZW compression to Unix systems, becoming the standard until gzip's arrival with better compression and no patent restrictions.

Key Milestones

  • 1985: compress utility released (Unix)
  • 1987: LZW patent issued (Unisys)
  • 1992: gzip replaces compress
  • 2003: LZW patent expired
  • 2010: Legacy format (rarely created)
  • Present: Historical archives only

Key Features

Core Capabilities

  • LZW Algorithm: Lempel-Ziv-Welch compression
  • Simple Format: Straightforward structure
  • Fast Compression: Quick processing (1980s standards)
  • Unix Native: Built-in compress/uncompress
  • Tar Compatible: .tar.Z archives
  • Legacy Support: Historical Unix systems

Common Use Cases

Legacy Archives

Old Unix backups (1980s-90s)

Vintage Systems

SunOS, HP-UX, AIX

Software

Historical software tarballs

Archival

Historical data preservation

Advantages

  • Historical Unix standard (1980s-90s)
  • Simple format (easy to implement)
  • Built-in Unix support (compress/uncompress)
  • Fast compression (1980s hardware)
  • gzip can decompress .Z files
  • LZW patent expired (no restrictions)
  • Widely used in legacy archives

Disadvantages

  • Obsolete (gzip/bzip2/XZ superior)
  • Lower compression ratio than modern formats
  • LZW patent issues (historical, expired 2003)
  • No longer created (legacy decompression only)
  • Limited modern tool support
  • Replaced by gzip in 1992

Technical Information

Format Specifications

Specification Details
File Extension .Z (uppercase), .tar.Z (tarball)
MIME Type application/x-compress
Algorithm LZW (Lempel-Ziv-Welch)
Released 1985 (Unix BSD)
Status Obsolete (replaced by gzip 1992)
Patent LZW expired 2003

Common Tools

  • Unix: compress (compress), uncompress (decompress)
  • Modern: gzip -d file.Z, gunzip file.Z
  • Cross-platform: 7-Zip, WinZip (Windows)
  • Replacement: gzip (.gz), bzip2 (.bz2), XZ (.xz) recommended