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| Filename extension | .rar, .rev, formerly .r00, .r01, etc. |
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| Internet media type | |
| Developed by | Eugene Roshal |
| Type of format | Archive format |
In computing, RAR is an 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: Roshal ARchive), and is currently licensed by Win.RAR GmbH.[1]
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.
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Versions
Several versions of the RAR format have been noted by third party developers:[2]
- RAR (original)
- RAR2
- RAR3 (current) – implemented by developers of Rarlab WinRAR version 2.9 and released in WinRAR version 3.00.[3] 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 text data, selective preprocessing algorithms based on platform and source file type.
- Option of 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 4 GB and Unicode names.
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
Mac OS X
- Read/Write: RAR (command line), Gumby 1.0b50, SimplyRAR
- Read-only: RAR Expander, Stuffit Expander, The Unarchiver, UnRarX, Zipeg, free unrar, non-free unrar
DOS
OS/2
FreeBSD
WinRAR
Roshal created the RAR file format and developed programs for packing and unpacking RAR files, originally for DOS,[citation needed] 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 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[4], although it is not under a free software license. 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.
The mostly free software archiver 7-Zip uses a proprietary plugin under the non-free "unRAR license" for decompression of newer RAR files.
Comparison to other compression algorithms
RAR compression operations are typically slower than compressing the same data with early compression algorithms like ZIP and gzip, but with a moderately better rate of compression.
7z's LZMA algorithm is quite similar to RAR in providing extremely high compression efficiency at the cost of computing time to compress and decompress. Both provide among the highest compression efficiency of any popular scheme, with the question of which algorithm is the more efficient compression scheme strongly depending on the files being compressed. Both formats are still being actively developed.
Features
Apart from the rate of compression, RAR has several other original features:
- It is able to efficiently handle split volumes. Before the advent of RAR the most notable such format was ARJ. Built-in support for multi-volume files enables the unpacking program to simply prompt the user for the next disk, without the need to manually copy and then rejoin the pieces, or for extracting a file from a single piece without needing all pieces. RAR does not support tapes, as it uses seek and rename operations on its files.
- Variable amounts of redundancy (“recovery record”) can be added to an archive, making it more resistant to corruption. Even if parts of an archive are damaged, it is possible to fully recover the stored data if a large enough recovery record exists.
- RAR archives can be of a solid format, in which all of the compressed files are treated as a single data block. Most currently used compression formats (with the exception of the older ZIP) allow solid structuring.
- It features strong encryption capabilities. Older versions of the file format used a proprietary algorithm; newer versions use the AES encryption algorithm, a block cipher adopted as an encryption standard by the U.S. government. The only known ways to recover an encrypted file are via dictionary or brute force attacks.
- In newer versions, password protection can optionally protect filenames too, so that the filenames contained within the archive will not be displayed without the right password.
- In Windows environments, it has the capability of storing NTFS streams and security information within the archive – information that is not stored in many other compression formats
- In OS/2 environments, RAR can handle extended attributes.
- RAR files can be embedded in other file types, probably the most common being JPEG. Image handling programs, browsers, and other utilities usually ignore any additional data after the end of the image, while RAR ignores anything before the RAR header. The procedure to create such a file is to append a RAR file to a JPEG. (e.g.: in DOS/Windows command-line: copy /b image1.jpg+something.rar image2.jpg, other variant: type something.rar >> image.jpg, in UNIX: cat something.rar >> image.jpg). [5][dead link]
Internet media type
Apache lists the default Internet media type for RAR files as application/x-rar-compressed.
See also
References
- ^ WinRAR download and support. WinRAR is a powerful Windows tool to compress and decompress zip, rar and many other formats: CONTACT
- ^ Home of unrarlib - UniquE RAR File Library
- ^ RAR and WinRAR Product Version History
- ^ http://www.rarlab.com/rar_add.htm - freeware UnRAR source and binaries download
- ^ [1]
External links
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