In
computing,
RAR is a
proprietary 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.
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.
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.
Versions
Several versions of the RAR format have been noted by third party developers:
- 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 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 author,
Alexander Roshal.
[The RAR Archiver EULA (End user license agreement) is embedded in installation files - ] RAR for Pocket PC is the only
freeware for creating RAR files.
Squeez is commercial software available only for Microsoft Windows that can read and write RAR files. It can write RAR 1.5 and RAR 2.0 files and supports basic encryption.
[http://www.speedproject.de/enu/squeez/]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)
available only 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, 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 "", 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.
The open source software archiver
7-Zip uses a proprietary plugin under the free and
source-available (but non-
free) "unRAR license" for decompression of newer RAR files. is a skinable freeware frontend for the Windows unrar DLL. 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.
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 generally both faster and has a better compression ratio than RAR, except for "multimedia" files like .wav and .bmp files where RAR will switch to specialized routines that outperform LZMA. Other free compression software such as
NanoZip and
FreeArc also usually outperform WinRAR.
For further reading see the
comparison of file archiver efficiency.
Internet media type
Apache lists the default
Internet media type for RAR files as
application/x-rar-compressed.
See also
