Gzip is used primarily for compressing and decompressing a file
to change the size so that it won't take up much room on a computer
without the need for an external archiver.
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The 'compress' command is normally supplied in all Unix and
Linux distributions. The Gzip protocol is also very common, as is
the original pkzip format.
7z is also used along with others, but those are the most
popular.
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Archives are smaller than with gzip. Compression requires more
resources though.