RAR (file format)

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.^[3]

File format

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.^[4]

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 exbibytes minus 1 byte.^[5]

Versions

The RAR file 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 changes:
  • Multimedia compression for true color bitmap images and uncompressed audio.
  • Up to 1 MiB compression dictionary.
  • Introduces archives data recovery protection record.
• v2.9^{[note 1]} - 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 of both file data and file headers.
  • Improves compression algorithm using 4 MiB 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 GiB.
  • Support for Unicode file names stored in UTF-16 little endian format.
• v5.0 - supported by WinRAR 5.0 and later. Changes in this version:
  • Maximum compression dictionary size increased to 1 GiB (default for WinRAR 5.x is 32 MiB and 4 MiB for WinRAR 4.x).
  • Maximum path length for files in RAR and ZIP archives is increased up to 2048 characters.
  • Support for Unicode file names stored in UTF-8 format.
  • Faster compression and decompression.
  • Multicore decompression support.
  • Greatly improves recovery.
  • Optional AES encryption increased from 128-bit to 256-bit.
  • Optional 256-bit BLAKE2 file hash instead of a default 32-bit CRC32 file checksum.
  • Optional duplicate file detection.
  • Optional NTFS hard and symbolic links.
  • Optional 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 at the end of the file that contains the names of files included, allowing archives to be opened faster.
  • Removes specialized compression algorithms for Itanium executables, text, raw audio (WAV), and raw image (BMP) files; consequently some files of these types compress better in the older RAR (4) format with these options enabled than in RAR5.

Notes

Software

Operating system support

Software is available for Microsoft Windows (named WinRAR), Linux, FreeBSD, macOS, and Android; archive extraction is supported natively in Chrome OS. WinRAR supports the Windows Graphical User Interface (GUI); other versions named RAR run as console commands. Later versions are not compatible with some older operating systems previously supported:

• WinRAR v5.x supports Windows XP and later.
• WinRAR v4.11 is the last version that supports Windows 2000.^[6]
• WinRAR v3.93 is the last version that supports Windows 95, 98, ME, and NT.^[6]
• RAR v3.93 is the last version that supports MS-DOS and OS/2 on 32-bit x86 CPUs such as 80386 and later. It supports long file names in a Windows DOS box (except Windows NT), and uses the RSX DPMI extender.^[7]
• RAR v2.50 is the last version that supports MS-DOS and OS/2 on 16-bit x86 CPUs such as Intel 8086, 8088, and 80286.^[7]

Creating RAR files

RAR files can be created only with commercial software WinRAR (Windows), command-line RAR (Windows, MS-DOS, macOS, Linux, Android,^[8] and FreeBSD), and other software that has written permission from Alexander Roshal or shares copyrighted code under license from Alexander Roshal. Only WinRAR for Windows and Rar for Linux are available as native 64-bit applications. The software license agreements forbid reverse engineering.^[3]

Extracting RAR files

Several programs can unpack the file format. As of November 2014 some 3rd-party programs documented as "supporting the RAR format" did not recognise RAR5 files.

• RARLAB distributes the C++ source code and binaries for a command-line "unrar" program.^[9] The license freely permits its use to produce software capable of unpacking, but not creating, RAR archives, but it is not an unrestricted free software license.
• The Unarchiver is a free software unarchiver for RAR and other formats, licensed under the LGPL. It runs on macOS and the command line version, unar, also runs on Windows and Linux. It supports all versions of the RAR archive format including RAR3 and RAR5.^[10][11][12]
• PeaZip is a free software RAR unarchiver for Windows, licensed under the LGPL, it also runs as RAR extractor on Linux and BSD, with GUI. PeaZip supports both pre-RAR5 .rar files, and files in new RAR5 format (out of the box). It can also install UNRAR5 Plugin based on royalty-free but not OSI-compliant RARLAB's unrar as alternative engine to handle RAR5 format.
• 7-Zip starting from version 15.06 beta^[13] can unpack RAR5 archives, using the RARLAB unrar code.
• UniquE RAR File Library (unrarlib),^[14] an older version of the unrar source was the basis for an obsolete free software unarchiving library called "unrarlib", licensed under the GPL. It could only decompress archives created by RAR versions prior to 2.9; archives created by RAR 2.9 and later use different formats not supported by this library. The original development team ended work on this library in 2007.^[15][16][14]

See also

• List of archive formats
• Comparison of archive formats
• Comparison of file archivers
• Data corruption, Bit rot, Disc rot

References

External links

• Official website
• RARLAB FTP download website, current and old versions of WinRAR and RAR
• RAR 5.0 archive file format