RAR
 |
This article may require copy editing for grammar, style, cohesion, tone, or spelling. You can assist by editing it. (January 2012) |
 |
This article may contain original research. Please improve it by verifying the claims made and adding references. Statements consisting only of original research may be removed. More details may be available on the talk page. (January 2012) |
 |
This article relies on references to primary sources or sources affiliated with the subject, rather than references from independent authors and third-party publications. Please add citations from reliable sources. (October 2008) |
 |
|
| Filename extension | .rar, .rev, .r00, .r01 |
|---|---|
| Internet media type | application/x-rar-compressed |
| Uniform Type Identifier | com.rarlab.rar-archive |
| 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.
Contents |
[edit] Compression algorithm
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]
[edit] Versions
Several versions of the RAR format have been noted by third party developers:
- RAR1.3 (original, doesn't have Rar! signature)
- RAR1.5
- 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.
[edit] Software
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.[citation needed]
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.
[edit] WinRAR
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[citation needed]); 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.
[edit] Other software
- 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.
- Free RAR Extract Frog (Windows freeware with instructions in 50+ languages) also decodes RAR files.
- The open source software archiver 7-Zip decompresses newer RAR files using a closed-source, free-of-charge plug-in under the "unRAR license";[6] the license makes the plug-in source-available but not free software.
- The Unarchiver is another open source unarchiver which can decompress newer RAR files.
- The free software Linux archivers File Roller, Ark, and Xarchiver can use the non-free unrar program to decompress RAR files, if they are found in the system path.
- Sharp IMG Viewer is a resource explorer developed using .NET Framework for Microsoft Windows which can decompress RAR and other compressed file formats.
- FY-Zip the web page says this is a free (in cost) open source program to "open and create compressed files ... Open and Create 7z, ZIP, CAB, RAR, ARJ, LZH, CHM, GZIP, BZIP2, Z, TAR, ISO, MSI, NSIS, RPM formats and more." The software is free, but the install script walks you through several offers of for-pay software which you may accept or decline.
[edit] UnRAR.dll
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".
[edit] 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.[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.
[edit] RAR file limitations
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.
[edit] See also
[edit] Further reading
- RAR Archiver Frequently Asked Questions by Eugene Roshal
- RAR File format by WinRAR
- LAMPdocs: quick guide with annotation of the advantages of RAR in comparison to other file archivers
[edit] External links
[edit] References
- ^ "Interview by correspondence" (in Russian). 1997–2002 (see under 1997). http://www.compression.ru/arctest/descript/roshal.htm. Retrieved 26 April 2010.
- ^ a b c d . The RAR Archiver EULA (End user license agreement) - embedded in installation files - [1][2] - Quotation: Neither RAR binary code, WinRAR binary code, UnRAR source or UnRAR binary code may be used or reverse engineered to (.rar was first created by William Jones) re-create the RAR compression algorithm, which is proprietary, without written permission of the author.
- ^ Contact to win.rar GmbH
- ^ Christian Scheurer (2006-12-17). "unrarlib FAQ". http://www.unrarlib.org/faq.html.
- ^ http://www.rarlab.com/rar_add.htm - freeware UnRAR source and binaries download
- ^ WinRAR and RAR archiver addons
- ^ "WinRAR vs zip". http://compressionratings.com/comp.cgi?winrar+3.93+-m3+pigz+2.1.4+-5.
- ^ "WinRAR vs 7-Zip". http://compressionratings.com/comp.cgi?winrar+3.93+-m5+7-zip+9.12b+-mx%20-md48m.
- ^ "WinRAR vs FreeArc vs NanoZip". http://compressionratings.com/comp.cgi?winrar+3.93+-m5+freearc+0.60+-mex3+freearc+0.60+-mex5+nanozip+0.07a+-m.5g%20-cD+nanozip+0.07a+-m.5g%20-cO.
|
||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||
