| Filename extension | .rar, .rev, .r00, .r01 |
|---|---|
| Internet media type | application/x-rar-compressed |
| Magic number | Rar! |
| Developed by | Eugene Roshal |
| Initial release | March 1993[1] |
| Type of format | archive format |
| Open format? | No |
RAR stands for Roshal ARchive. It is a proprietary[2] archive file format that supports data compression, error recovery, and file spanning. It was developed by a Russian software engineer, Eugene Roshal (the first letter of his surname contributing to the name of the archive format), and is currently licensed by win.rar GmbH.[3]
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 split into many smaller files (a "multi-volume archive"), the smaller files used the extensions .rar, .r00, .r01, .r02 etc.
Version 1 and 2 archive files were often used in conjunction with a parchive file archiver to create parity files for error recovery when using less-than-perfect file transmission and storage media such as newsgroups, satellite transmission, and optical discs. Version 3 has eliminated the need for third party post-processing.
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The RAR compression utility is proprietary, with a closed algorithm. RAR is owned by Alexander L. Roshal,[2] the elder brother of Eugene Roshal. Version 3 of RAR is based on Lempel-Ziv (LZSS) and prediction by partial matching (PPM) compression, specifically the PPMd implementation of PPMII by Dmitry Shkarin.[4]
Several versions of the RAR format have been noted by third party developers:
RAR files may be created only with commercial software WinRAR, RAR, and software that has permission from the licensor Alexander Roshal (Eugene's brother).[2] RAR for Pocket PC is the only freeware for creating RAR files.
Third-party programs that can only read (unpack) RAR files include: WinZip (Windows), RarZilla (Windows), 7-Zip (multiplatform), IZArc (Windows), PeaZip (Windows, Linux), Zipeg (Windows, Mac OS X), ALZip (Windows) and PowerArchiver (Windows), along with the free version of unrar (which is available for Linux and FreeBSD). Mac OS X readers include StuffIt Expander, The Unarchiver, UnRarX, and Zipeg. Stuffit Expander is also available for Mac OS Classic with RAR support for this platform.
WinRAR is commercial software (or 40-day trial)[2] available for Microsoft Windows. It is the only graphical tool that can write modern RAR files (RAR version 3). WinRAR's command line equivalent, RAR, is also commercial software (or 40-day trial), available for Windows, Linux, Mac OS X, MS-DOS, OS/2, and FreeBSD. Additionally, the unrar tool from the same distributor can be used on the aforementioned platforms to extract RAR files but not to write them.
Roshal created the RAR file format and developed programs for packing and unpacking RAR files, originally for DOS in 1993, which were later ported to other platforms. The main Windows version of the archiver, known as WinRAR, is distributed as trialware, requiring payment after 40 days (although it can still be used after this period, albeit with nags); shareware versions of this program are also available for GNU/Linux, Mac OS X, DOS, OS/2, and FreeBSD, though they are all called simply "RAR".
RARLAB distributes the source code and binaries for a freeware command-line "unrar" program,[5] although it is not under a free software license. This program can only decompress/extract, not create RAR files.
UnRAR.Dll is a free of charge dynamic-link library (DLL) that can be downloaded from the official WinRAR site. It is found under "Extras".
RAR compression operations are typically slower than compressing the same data with early compression algorithms like ZIP but with a moderately better rate of compression.[7]
7z's LZMA algorithm reaches a higher compression ratio than RAR, except for "multimedia" files like .wav and .bmp files where RAR uses specialized routines that outperform LZMA.[8] Other free compression software such as NanoZip and FreeArc usually outperform WinRAR.[9]
Optional creation of "recovery volumes" (.rev files) with redundancy data which can be used to reconstruct missing files in a volume set.
The minimum size of a RAR file is 20 bytes. The maximum size of a RAR file is 9,223,372,036,854,775,807 (263-1) bytes, which is 8 exabytes.
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