RAR (file format): Difference between revisions

RAR
	File:Multiple
Filename extension	.rar, .rev, .r00, .r01
Internet media type	application/x-rar-compressed
Uniform Type Identifier (UTI)	com.rarlab.rar-archive
Magic number	Rar!
Developed by	Eugene Roshal
Initial release	March 1993
Type of format	archive format
Free format?	No

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RAR 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 name RAR stands for Roshal ARchive) and the software is currently 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.

The RAR compression utility is proprietary software, to which Alexander L. Roshal,^[2] 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 exabytes.

Versions

Rar - Introduction

In computer science, RAR is a file compression and archiving of the proprietary format.The name RAR is derived from its author Eugene Roshal, Roshal ARchive.Eugene Roshal initially prepared a version of DOS encoding and decoding procedures, later ported to many platforms, such as the famous Windows WinRAR platform.Eugene Roshal conditional discloses decoding program source code, but the code is still proprietary.

RAR format by WinRAR, WinMount and other software to open RAR file extensions are.Rar, MIME type of application/x-rar-compressed.It is a lossless data compression, RAR file is usually better than ZIP file compression ratio to be high, but the compression speed is slower .Because the RAR file header will occupy a certain space, in a little room for data compression, the compressed file can be greater than the original file.A major advantage of RAR is file compression target segmentation into multiple files, and easily from such a segmentation of the compressed files unpacked source file.In addition, RAR also supports compression format, all the files compressed into the same data area so as to increase the compression ratio, at the cost of extracting a single file must be unpacked in front of all the files.The new RAR encryption algorithm used is AES, while the old RAR encryption algorithm is private.These two algorithms are very difficult to crack, so there is no password only in case of using the dictionary brute force method to crack.RAR can also join the redundant information in the file is damaged but repaired, the repair information sufficiently intact to compress a bag to repair.^[5] Several versions of the RAR format have been noted by third party developers:

RAR1.3 (original, does not 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 was changed from cipher block chaining (CBC) mode 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. being $ubashish

Software

The only software capable of creating RAR files are WinRAR, RAR, and software that shares copyrighted code under license from Alexander Roshal (Eugene's brother). The software license agreements forbid reverse engineering.^[2]

There are several programs capable of unpacking the file format. RARLAB itself 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.

An older version of the unrar source is the basis for a free software decompression library called "unrarlib", licensed under the GPL, 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.

External links

Official RAR site

References

^ "Interview by correspondence" (in Russian). 1997–2002 (see under 1997). Retrieved 26 April 2010. {{cite web}}: Check date values in: |date= (help)
^ ^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.
^ Contact to win.rar GmbH
^ Christian Scheurer (2006-12-17). "unrarlib [[FAQ]]". {{cite web}}: URL–wikilink conflict (help)
^ Hudong baike
^ "freeware UnRAR source and binaries download". RarLab.com.

[1] "Interview by correspondence" (in Russian). 1997–2002 (see under 1997). Retrieved 26 April 2010. {{cite web}}: Check date values in: |date= (help)

[rar_eula-2] 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.

[3] Contact to win.rar GmbH

[4] Christian Scheurer (2006-12-17). "unrarlib [[FAQ]]". {{cite web}}: URL–wikilink conflict (help)

[5] Hudong baike

[6] "freeware UnRAR source and binaries download". RarLab.com.

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@@ Line 51: / Line 51: @@
 **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.
+**Support for Unicode names. being $ubashish
 == Software ==

v t e Archive formats
Archiving only	ar cpio shar tar LBR WAD WARC
Compression only	Brotli bzip2 compress gzip Zopfli LZMA LZ4 lzip lzop SQ xz Zstandard
Archiving and compression	7z ACE ARC ARJ B1 Cabinet cfs cpt dar DGCA .dmg .egg kgb LHA lrzip LZX MPQ PEA RAR rzip sit sitx SQX UDA Xar zoo ZIP ZPAQ
Software packaging and distribution	apk App APPX deb HAP ipa JAR WAR Java RAR EAR MSI MSIX Package (macOS) RPM XAP XBAP
Document packaging and distribution	OEB Package Format OEBPS Container Format Open Packaging Conventions PAQ
Comparison List Category