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RAR is a patented archive file format that supports data compression, error recovery, and file spanning. RAR archives are able to handle efficiently split volumes. Before the advent of RAR the most notable such format was ARJ. It can be of a solid format, in which all of the compressed files are treated as a single data block.
The filename extension used by RAR is .rar for the data volume set and .rev for the recovery volume set. In previous versions, if a RAR-archive was broken into many smaller files (a "multi-volume archive"), then the smaller files used the extensions .rar, .r00, .r01, .r02 etc.It can be of a solid format, in which all of the compressed files are treated as a single data block.