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compress (.Z) file format

.Z  ·  compression (single file)  ·  introduced 1984 by Spencer Thomas / Joseph Orost

What is a compress (.Z) file?

compress is the original Unix file compressor, released in 1984. It uses LZW (the same algorithm as GIF) and produces .Z files. LZW patent issues led directly to the creation of GZIP as a free replacement; .Z files are now legacy.

Most readers reach this page after double-clicking a .Z file and finding their operating system unsure what to do with it. The good news: compress (.Z) is a well-understood format with mature tooling on every major platform. It is supported in one click by mainstream archivers on Windows, macOS, and Linux.

How to extract a compress (.Z) file

Opening a .Z file is straightforward on every modern operating system. The exact steps depend on which platform you are on:

On Windows

  1. Locate the .Z file in File Explorer.
  2. Right-click the file. If you have 7-Zip installed, choose 7-Zip → Extract Here. On Windows 11 the built-in extractor handles ZIP, 7z, RAR and several other formats directly through Extract All…
  3. If prompted, pick a destination folder and click Extract.
  4. The extracted files appear in a folder next to the original archive.

On macOS

  1. Find the .Z file in Finder.
  2. Install The Unarchiver from the Mac App Store, or Keka for both creating and extracting.
  3. Right-click the file → Open With → The Unarchiver (or just double-click after Unarchiver is set as the default).
  4. The extracted folder appears next to the archive.

On Linux

  1. Use your file manager: right-click the archive → Extract Here (file-roller on GNOME, Ark on KDE).
  2. On the command line, run one of: 
    7z x archive.Z    # works for almost any format
  3. The files appear in the current directory.

How to create a compress (.Z) file

To pack files into a .Z archive, you typically need an archiver that supports writing this format. Not every tool can create every format — for example, only WinRAR can create real RAR files. The sidebar lists the software known to read and write compress (.Z).

On the command line, the canonical create command is:

# Use 7-Zip, PeaZip, or the format's reference tool to create .Z files.

If you regularly create archives at scale, a dedicated archive automation suite can wrap this command in scheduled jobs, integrity checks, and offsite replication.

Strengths

  • Tiny, fast

Weaknesses and limitations

  • Weak compression
  • Legacy LZW algorithm
  • Largely retired

Typical use cases

  • Vintage Unix man pages
  • Legacy Solaris software
  • Old USENET archives

Technical details

compress (.Z) uses the LZW algorithm and is identified on disk by the magic byte sequence 1F 9D. The standard MIME type is application/x-compress. The format is an open specification and is free for any use.

Frequently asked questions

Is compress (.Z) safe to open?

Archive files are containers — they are only as safe as what they contain. A .Z from a trusted source is fine; one received from a stranger can hold malicious executables, scripts, or files engineered to exploit bugs in your archiver. Always keep your archiver updated, and never run unknown executables that come out of an archive. A safe workflow is to extract into a sandbox and scan the contents before opening anything.

What is the maximum file size?

Modern implementations support archives in the multi-terabyte range. The practical limit is your filesystem (FAT32 caps at 4 GB; ext4, NTFS, APFS, and exFAT all comfortably handle multi-TB files).

Can I password-protect a compress (.Z)?

Some archivers can wrap compress (.Z) files in an encrypted container, but the format itself does not always include built-in encryption. Check your archiver's documentation.

How does compress (.Z) compare to other formats?

See our format comparison pages such as ZIP vs 7z, ZIP vs RAR, and tar.gz vs tar.xz for side-by-side feature tables.

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