Z File Format (.z)
A Z file is a single stream compressed with the LZW algorithm by the Unix compress utility, the format gzip was written specifically to replace once a patent on LZW made distributing compress a legal risk.
Z at a glance#
| Full name | compress archive |
|---|---|
| File extension | .z |
| Category | Archives |
| Developer | Spencer Thomas |
| First released | 1984 |
| MIME types | application/x-compress |
| Compression | Lossless |
| FileFlip support | FileFlip reads and writes this format |
What a .z file can hold#
These are the things a Z file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.
| Streaming | Yes |
|---|
Strengths and limitations of Z#
What Z does well
- LZW decompression is cheap even on old or slow hardware
- Was the standard Unix compressor before gzip existed, so archives that old still turn up readable
Where Z falls short
- Compression ratio is clearly worse than gzip, let alone bzip2 or xz, and the format has been obsolete for that reason for decades
- Rarely supported out of the box anymore; many modern tools need a plugin or a separate uncompress utility
- Compresses a single file or stream only, with no archiving of multiple files
There's essentially no reason to create a new Z file today; gzip replaced it decades ago with better compression and no patent risk.
Convert an old Z file to GZ or XZ so modern tools that dropped compress support can actually open it.
How to open a .z file#
A .z file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts Z into a format your machine already opens, and it does it in the browser tab rather than on a server.
| Platform | Programs that open it |
|---|---|
| Windows | 7-Zip |
| macOS | The Unarchiver |
| Linux | gzip (terminal) |
| Web | FileFlip |
Z questions people ask#
Is a .Z file the same as gzip?
No. A .Z file is compressed with the older Unix compress utility's LZW algorithm, not gzip's DEFLATE, and the two aren't interchangeable; a tool built to read .gz files can't decompress a .Z file.
Why was Unix compress replaced by gzip?
Unix compress used the LZW algorithm, which Sperry, later Unisys, held a patent on, and the resulting licensing risk pushed the Free Software Foundation to write gzip as a patent-free, better-compressing replacement in 1992. Compress fell out of use well before the LZW patent itself expired in 2003.
Can modern tools still open a .Z file?
Many can: gzip itself can decompress .Z files even though it can't create them, and tools like 7-Zip and The Unarchiver read the format too. Native support has thinned out over the decades, so an old .Z file that a tool won't open usually just needs a dedicated uncompress utility or a converter.
Converting Z files#
Convert Z to another format
Convert another format to Z
Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.