RAR (file format) Totally Explained

Everything about Rar totally explained

In computing, RAR is a patented archive file format that supports data compression, error recovery, and file spanning. It was developed by Eugene Roshal (hence the name RAR: Roshal ARchive) and currently licensed by Win.RAR GmbH(External Link

) 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 3rd party post-processing.

Versions

Several versions of the RAR format have been noted by 3rd party developers:(External Link

)

RAR (original)
RAR2
RAR3 (current) – implemented by developers of Rarlab WinRAR version 2.9 and released in WinRAR version 3.00.(External Link) Many changes including:
- File extensions changed from .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

Read/Write: RAR

Read-only: free unrar, non-free unrar

Mac OS X

Read/Write: RAR (command line), SimplyRAR

Read-only: RAR Expander, Stuffit Expander, UnRarX, Zipeg, free unrar, non-free unrar

DOS

RAR, non-free unrar

OS/2

RAR, non-free unrar

FreeBSD

RAR, free unrar, non-free unrar

WinRAR

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 Linux, Mac OS X, DOS, OS/2, and FreeBSD, though they're all called simply "RAR".
RARLAB distributes the source code and binaries for a freeware command-line "unrar" program, although it isn't 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 isn't 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

ť Note that compression performance is hard to compare, as it heavily depends on the kind of data being compressed. The statements in this paragraph apply to "typical" data (text, software binaries, productivity software files). See also the section on efficiency in Comparison of file archivers.

RAR compression operations are typically much slower than compressing the same data with early compression algorithms like ZIP and gzip, but with a much 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 handle efficiently split volumes. Before the advent of RAR the most notable such format was ARJ. It is unnecessary to use split volumes for this purpose alone since just binary splitting the files will work fine, and they can be reassembled with cat or binary copy. Multi-volume files have wide use though, mainly because they're generally easier to handle, especially when the file is spanning multiple disks. Built-in support for multi-volume files enable 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. Unfortunately, RAR doesn't 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's 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, which are usually infeasible with non-dictionary passphrases starting from 8 characters.

In newer versions password protection can optionally protect filenames too, so that the files contained within the archive won't 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's usually lost on compression.

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. (for example: in DOS/Windows command-line: copy /b image1.jpg+something.rar image2.jpg, in UNIX: cat something.rar >> image.jpg). (External Link

)

Internet media type

Apache lists the default Internet media type for RAR files as application/x-rar-compressed.

Further Information

Get more info on 'Rar'.

External Link Exchanges

Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:

<a href="http://rar__file_format.totallyexplained.com">RAR (file format) Totally Explained</a>

Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned.