What is the difference between the various ZIP formats: ZIP, GZIP, and PKZIP?
• A. GZIP files (the Gnu format) are not archives and compress only one file. GZIP is essentially a one file subset of the Zip format. Zip is an archive file format, popularized on PCs, that contains multiple compressed files. PKZIP is a set of commercially-available programs that create Zip files. All three PKZIP, GZIP and Zip use the deflate compression format, which is based on the LZ77 algorithm. This compression is also used by the ZLIB library and hence the PNG graphics file format (which uses ZLIB). PNG – Portable Network Graphics – provides a patent-free replacement for GIF and TIFF. If you save a GIF, don’t forget to pay the royalty to Unisys — see Unisys’s web page at http://www.unisys.com/LeadStory/lzwfaq.html. That patent is why GIFs should not be used. The PNG format is specified in RFCs 1950, 1951, and 1952, and is unencumbered by licenses or patents. An alternative compression technology, LZW compression, is encumbered by Unisys’s patent. LZW is used in GIF files and by
