Gzip is a compression program; it will take a single file and reduce the amount of space it requires to make for faster transfer or more efficient archiving. It is often used in conjunction with some flavor of tar. It includes software for both compressing and decompressing, and can handle its own native gzip format in addition to the older compress format. The gzip format is extremely popular online, and tends to be more efficient than the zip format but less efficient than the bzip2 format. Gzip is available for all flavors of UNIX, both flavors of Mac OS, most flavors of MS-Windows, and MS-DOS.