Rar Extension

In computing, RAR is a proprietary archive file format that supports data compression, error recovery, and file spanning. It was developed by a Russian software engineer, Eugene Roshal (hence the name RAR: R oshal AR chive), and is currently licensed by win.rar GmbH .

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.

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.

Compression algorithm

Version 3 of RAR is based on Lempel-Ziv and prediction by partial matching (PPM) compression, specifically the PPMd implementation of PPMII by Dmitry Shkarin.

Versions

Several versions of the RAR format have been noted by third party developers:

• RAR (original)
• RAR2
• RAR3 (current) – implemented by developers of Rarlab WinRAR version 2.9 and released in WinRAR version 3.00. Many changes including:
  • File extensions changed from {volume name}.rar, {volume name}.r00, {volume name}.r01, etc. to {volume name}.part001.rar, {volume name}.part002.rar, etc.
  • Encryption algorithm is changed to AES (Advanced Encryption Standard) with 128 bit key length.
  • Encryption of both file data and file headers.
  • Improved compression algorithm using 4MB dictionary size, Dmitry Shkarin's PPMII algorithm for file data, and selective preprocessing algorithms based on platform and source file type.
  • Optional creation of "recovery volumes" (.rev files) with redundancy data which can be used to reconstruct missing files in a volume set.
  • Support for archive files larger than 9 GB.
  • Support for Unicode names.

Software

RAR files may be created only with commercial software WinRAR, RAR, and software that has permission from the author, Alexander Roshal. RAR for Pocket PC is the only freeware for creating RAR files.

Squeez is commercial software available only for Microsoft Windows that can read and write RAR files. It can write RAR 1.5 and RAR 2.0 files and supports basic encryption.

Third party programs that can only read (unpack) RAR files include: WinZip (Windows), 7-Zip (multiplatform), IZArc (Windows), PeaZip (Windows, Linux), Zipeg (Windows, Mac OS X), ALZip (Windows), along with the free version of unrar (which is available for Linux and FreeBSD). Mac OS X readers include Stuffit Expander, The Unarchiver and Zipeg. Stuffit Expander is also available for Mac OS Classic with RAR support for this platform.

WinRAR

Main article: WinRAR

WinRAR is commercial software (or 40-day trial) available only 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, 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, although it is not under a free software license. This program can only decompress/extract, not create RAR files.

Other programs

There is a free software decompression library called "unrarlib", licensed under the GPL, based on an old version of unrar with permission from the author Eugene Roshal, but it can only decompress archives created by RAR versions up to 2.x. Archives created by RAR 2.9 and later (which are most RAR archives found today) use a different format which is not supported by the free library.

Stuffit Expander (freeware associated with the paid-for Stuffit compression program) also decodes RAR files.

The open source software archiver 7-Zip uses a proprietary plugin under the free and source-available (but non-free) "unRAR license" for decompression of newer RAR files. Free RAR Extract Frog is a skinable freeware frontend for the Windows unrar DLL. The free software Linux archivers File Roller, Ark, and Xarchiver can use the non-free unrar program to decompress RAR files, if it is found in the system path.

Comparison to other compression algorithms

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.

7z's LZMA algorithm reaches higher compression ratio than RAR, except for "multimedia" files like .wav and .bmp files where RAR will switch to specialized routines that outperform LZMA. Other free compression software such as NanoZip and FreeArc usually outperform WinRAR.

For further reading see Compression comparison.

Internet media type

Further information: MIME

Apache lists the default Internet media type for RAR files as application/x-rar-compressed .

See also

• List of archive formats
• Comparison of file archivers

References

1. ^ ^{a b c} The RAR Archiver EULA (End user license agreement) is embedded in installation files -
2. ^ Contact to win.rar GmbH
3. ^ Christian Scheurer (2006-12-17). "unrarlib FAQ" . http://www.unrarlib.org/faq.html .  
4. ^ Home of unrarlib - UniquE RAR File Library
5. ^ RAR and WinRAR Product Version History
6. ^ http://www.speedproject.de/enu/squeez/
7. ^ http://www.rarlab.com/rar_add.htm - freeware UnRAR source and binaries download
8. ^ http://www.rarlab.com/rar_add.htm
9. ^ "WinRAR vs gzip" . http://compressionratings.com/comp.cgi?gzip+1.2.4++WinRAR+3.80+-s%20-m1 .  
10. ^ "WinRAR vs 7-Zip" . http://compressionratings.com/comp.cgi?7-Zip+9.01a+-mx%20-md48m+7-Zip+9.01a+-mx1%20-md48m+WinRAR+3.80+-s%20-m1+WinRAR+3.80+-s%20-m5 .  
11. ^ "WinRAR vs NanoZip vs FreeArc" . http://compressionratings.com/comp.cgi?WinRAR+3.80+-s%20-m3+WinRAR+3.80+-s%20-m5+NanoZip+0.07a+-m.5g%20-cD+NanoZip+0.07a+-m.5g%20-cO+FreeArc+0.50a+-m3+FreeArc+0.50a+-m6 .  

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