SZIP is a freeware portable general purpose lossless compression program. It has a high speed and compression, but high memory demands (up to 20MB) too. See the monthly Archive Comparison Test (A.C.T.) by Jeff Gilchrist for comparative results. Also check the Canterbury Corpus where szip is best compressor for large text files.

szip is not to be confused with the following:
SuperZip by ASTEC International
Compressed String Constants for Linux by Paul Russell
Science data lossless compression/decompression software by the University of New Mexico (uses a rice code and no blocksort)
Above was accepted by CCSDS (Consultative Committee on Space Data Systems) for use with space images. Note that Michael Schindler ownsthe trademark for the word szip in conjunction with compression and used it before them.

Recent improvements

Speed for large files is enhanced in 1.12a if the memory management of the OS is stupid. For example a 250MB file compressed with -o4b41 compressed with 1.11 in 22 minutes, with 1.12a in 3.5 minutes - that is more than 6 times faster.

Known problems

Inside szip there is no limitation to the file size, however your IO library or the one used for the compilation may fail on files larger than 2GB or 4GB. If you encounter this or other problems please contact

1.11 and 1.12 still print 1.11BETA as version (with the -v option).

1.11 and 1.12 may take longer than necessary because the operating system memory management will punish cooperative programs. Fixed in 1.12a

With -o0 VERY LONG runtimes for some files can happen. This is expected behavior of the public version. Don't use -o0 if this hurts you.

A popular webbrowser that comes with one PC operating system downloads .tar.gz as _tar.tar files - please fix this "feature" when asked for the filename.


szip [-d] [options] [inputfile [outputfile]]

If you omit the outputfile the result is sent to stdout. If you omit the inputfile too it reads from stdin. Since DOS/Windows/OS2 does not support binary pipes I recommend using both arguments in DOS/Windows/OS2.'s disclaimer

We have ported SZIP to a variety of platforms, that are in our download section.

We offer limited support for these ports, however, we do not offer support or download of other versions

If you want to download other version or need support for them, please contact directly with Michael Schindler at