RAR

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RAR
Filename extension .rar, .rev, .r00, .r01
Internet media type application/x-rar-compressed
Uniform Type Identifier com.rarlab.rar-archive
Magic number 52 61 72 21 1A 07 00
(RAR 1.5 to 4.0)
52 61 72 21 1A 07 01 00
(RAR 5+) [1]
Developed by Eugene Roshal
Initial release March 1993 [2]
Type of format archive format
Open format? Partially (open source decompression is available)

RAR is a proprietary[3] archive file format that supports data compression, error recovery and file spanning. It was developed by a Russian software engineer, Eugene Roshal (the name RAR stands for Roshal ARchive) and the RAR software is licensed by win.rar GmbH.[4]

File format[edit]

The filename extensions used by RAR are .rar for the data volume set and .rev for the recovery volume set. Previous versions of RAR split large archives into several smaller files, creating a "multi-volume archive". Numbers were used in the file extensions of the smaller files to keep them in the proper sequence. The first file used the extension .rar, then .r00 for the second, and then .r01, .r02, etc.

RAR compression applications and libraries (including GUI based WinRAR application for Windows, console rar utility for different OSes and others) are proprietary software, to which Alexander L. Roshal,[3] the elder brother of Eugene Roshal, owns the copyright. 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.[5]

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 minus 1 byte.[6]

Versions[edit]

The RAR format revision history:

  • v1.3 (original, does not have "Rar!" signature)
  • v1.5
  • v2.0 - released with WinRAR 2.0 and Rar for MS-DOS 2.0 features the following most notable changes:
    • Multimedia compression for true color bitmap images and uncompressed audio.
    • Up to 1MB compression dictionary.
    • Introduces archives data recovery protection record.
  • v2.91 - released in WinRAR version 3.00. Feature changes in this version include:
    • File extensions is 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 from cipher block chaining (CBC) mode to Advanced Encryption Standard (AES) with 128-bit key length.
    • Encryption of both file data and file headers.
    • Improves compression algorithm using 4MB dictionary size, Dmitry Shkarin's PPMII algorithm for file data,
    • 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 file names.
  • v5.0 - supported by WinRAR 5.0 and later. Changes in this version:
    • Up to 1GB dictionary.
    • Faster compression and decompression.
    • Multicore decompression support.
    • UTF-8 filenames.
    • 256-bit AES encryption.
    • New file hashing algorithm (BLAKE2).
    • Files duplicates detection.
    • Removes specialised text, multimedia and Itanium executables compression algorithms; consequently some files of these types compress better with WinRAR 4.2 (Rar4) than WinRAR 5.0 (Rar5).
    • Greatly improves recovery.
    • Supports NTFS hard and symbolic links.
    • Quick Open Record - Rar4 archives had to be parsed before opening as file names were spread throughout the archive, slowing operation particularly with slower devices such as optical drives, and reducing the integrity of damaged archives. Rar5 can optionally create a "quick open record", a special archive block containing the names of files included, allowing archives to be opened faster.

1 WinRAR 5.0 refers to this format as RAR4.

Software[edit]

Creating RAR files[edit]

RAR files can be created only with commercial software WinRAR, RAR, and other software that has written permission from Alexander Roshal or shares copyrighted code under license from Alexander Roshal. The software license agreements forbid reverse engineering.[3] Graphical WinRAR application is available only for Windows. Console RAR application is available for Mac OS X, Linux, FreeBSD. Only WinRAR for Windows and Rar for Linux are available as native 64bit applications. There is a native fully functional Android application called "RAR for Android".[7]

Extracting RAR files[edit]

Several programs can unpack the file format. RARLAB distributes the source code and binaries for a freeware command-line "unrar" program,[8] although this code is not under a free software license. This program can decompress/extract, but not create, RAR files.

The Unarchiver is a free software unarchiver for RAR and other formats, licensed under the LGPL. It runs on Mac OS X and the command line version, unrar, also runs on Windows and Linux. It supports all versions of the RAR archive format including RAR3.[9][10]

7-Zip and PeaZip are free software RAR unarchivers for Windows, both licensed under the LGPL. PeaZip also runs as RAR extractor on Linux and BSD, with GUI. p7zip (LGPL), the command line POSIX port of 7-Zip project runs on all Unix systems and it is used as RAR extractor by various graphical frontend applications.

An older version of the unrar source was the basis for an obsolete free software unarchiving library called "unrarlib", licensed under the GPL, but it could only decompress archives created by RAR versions prior to 2.9. Archives created by RAR 2.9 and later use a different format that is not supported by this library.

See also[edit]

References[edit]

  1. ^ RAR 5.0 technote
  2. ^ "Interview by correspondence" (in Russian). 1997–2002 (see under 1997). Retrieved 26 April 2010. 
  3. ^ a b c The RAR Archiver EULA (End user license agreement) - embedded in installation files - [1][2] - states: Neither RAR binary code, WinRAR binary code, UnRAR source or UnRAR binary code may be used or reverse engineered to re-create the RAR compression algorithm, which is proprietary, without written permission of the author.
  4. ^ Contact to win.rar GmbH
  5. ^ Christian Scheurer (2006-12-17). "unrarlib FAQ". 
  6. ^ "WinRAR description". Retrieved 2013-05-01. 
  7. ^ https://play.google.com/store/apps/details?id=com.rarlab.rar
  8. ^ "freeware UnRAR source and binaries download". RarLab.com. 
  9. ^ The Unarchiver Website contains unar. Accessed 5 February 2013.
  10. ^ Free Software Foundation on The Unarchiver

External links[edit]