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RAR
The Unarchiver rar.png

A rar archive icon from The Unarchiver's icon set.
Filename extension .rar, .rev, .r00, .r01.
Internet media type application/x-rar-compressed
Developed by Eugene Roshal
Type of format Archive format

RAR is a proprietary archive file format that supports data compression, error recovery, and file spanning.[1] 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.[2]

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.

Contents

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.[3]

Versions

Several versions of the RAR format have been noted by third party developers:[4]

  • RAR (original)
  • RAR2
  • RAR3 (current) – implemented by developers of Rarlab WinRAR version 2.9 and released in WinRAR version 3.00.[5] 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 licensor, Alexander Roshal (Eugene's brother).[1] 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), 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

WinRAR is commercial software (or 40-day trial)[1] 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 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,[6] 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.

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 proprietary plug-in free of charge under the "unRAR license";[7] the license makes the plug-in source-available but not free software. 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.

UnRAR.Dll

Is a free of charge Dll and Library that can be downloaded from the official WinRAR site. It is found under Extras.

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. [8]

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.[9] Other free compression software such as NanoZip and FreeArc usually outperform WinRAR.[10]

For further reading see Compression comparison.

Internet media type

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

See also

References

External links


Simple English

RAR
File extension:.rar, .rev, formerly .r00, .r01, etc.
MIME type:application/x-rar-compressed application/octet-stream
Developed by:Eugene Roshal
Type of format:Archive format

In computing, RAR is a patented[needs proof] archival file format that allows data compression, error recovery, and file spanning. It was created by Eugene Roshal (that is why it is named RAR: Roshal ARchive) and is now license to Win.RAR GmbH[1].

Contents

RAR File Archiver Software

The following is an example of file archiver software by platforms. For a comprehensive list see Comparison of file archivers

Windows

  • Read/Write: WinRAR
  • Read-only: 7-Zip, BitZipper, IZArc, PeaZip, RarZilla, Zipeg, free unrar, non-free unrar

Linux

  • Read/Write: RAR
  • Read-only: free unrar, non-free unrar

Mac OS X

  • Read/Write: RAR (command line), SimplyRAR
  • Read-only: RAR Expander, Stuffit Expander, UnRarX, Zipeg, free unrar, non-free unrar

DOS

  • RAR, non-free unrar

OS/2

  • RAR, non-free unrar

FreeBSD

  • Read/Write: rar, Ark (as frontend to rar)
  • Read Only: 7-Zip, free unrar, non-free unrar

References








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