7-Zip

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7-Zip

7-Zip archiver
Developer:	Igor Pavlov
Latest release:	4.42 / May 14, 2006
Preview release:	4.44 / January 20, 2007
OS:	Microsoft Windows, DOS, Linux, others
Use:	File archiver
License:	LGPL
Website:	www.7-zip.org

7-Zip is an open source file archiver designed originally for the Microsoft Windows operating system, and later made available to other systems. In the form of p7zip, 7-Zip has been ported for use on Unix-like systems such as Linux and FreeBSD. It is also compatible with DOS via either a DOS port, or by using the HX-DOS extender to run the Windows command-line version.

7-Zip operates primarily with 7z archive format, as well as being able to read several other archive formats. In operation a user is free to use command line (all systems), graphical user interface ("Windows" only) or seamless MS Windows shell environment methods of control.

7-Zip began in 2000 and is actively developed by Igor Pavlov. It is distributed under the terms of GNU Lesser General Public License (LGPL). As free software the program is free to share and comes with modifiable source code in contrast to the market-leading programs WinZip and WinRAR, which remain as proprietary competitors. Note that 7-Zip still uses a proprietary plugin to read RAR archives.

1 The 7z archive format
2 Other supported formats
3 Variations
4 Features
5 See also
6 External links

[edit] The 7z archive format

Main article: 7z

By default, 7-Zip is used to create 7z format archives, with a .7z file extension. Each archive can contain multiple directories and files. As a container format, security or size reduction are achieved using a stacked combination of filters. These can consist of pre-processors, compression algorithms and encryption filters.

The core .7z compression stage uses a variety of algorithms, the most common of which are Bzip2 and LZMA. Developed by Igor Pavlov, LZMA is a relatively new system, making its debut as part of the 7z format. LZMA consists of a large LZ-based sliding dictionary up to 4GB in size, backed by a range coder.

LZMA compression ratios tend to be very good. Compressed sizes are comparable to other high gain compression formats, including RAR or ACE, both of which are proprietary.

The native 7z file format is open and modular with all filenames stored as Unicode.

[edit] Other supported formats

7-Zip supports a number of other compression, and non-compression, archive formats. Supported formats include ZIP, Microsoft cabinet (CAB) files, RAR, ARJ, Z, gzip, bzip2, LHA, tar, cpio, rpm and Debian deb archives. Versions of 7-Zip from 4.42 onwards also support ISO CD/DVD images.

7-Zip is able to open MSI files, allowing access to the meta-files within along with the main contents. Some Microsoft CAB (LZX compression) and NSIS (LZMA) installer formats can be opened, making 7-Zip a good tool to check if a given binary file is in fact an archive.

When compressing ZIP or gzip files, 7-Zip uses a home-brewed DEFLATE encoder which is often able to achieve higher compression levels than the de facto zlib implementation, at the expense of compression speed. The 7-Zip deflate encoder implementation is available separately as part of the AdvanceCOMP suite of tools.

[edit] Variations

In the form of p7zip, the command-line version has been ported for use on Unix-like systems including Linux and FreeBSD.

A 64-bit version is available for Windows XP Professional x64 Edition, with support for large memory maps leading to faster compression. All versions support multi-threading.

Two command line versions are provided: 7z.exe, using external libraries; and a stand alone 7za.exe version which contains built-in modules. However, 7za's compression/decompression support is limited to 7z, ZIP, gzip, bzip2, Z and tar formats.

Additionally, a portable version of 7-Zip exists as well. This version runs completely from an external portable drive such as a USB thumb drive or an MP3 player like an iPod. It is available from portableapps.com (link below).

[edit] Features

7-Zip supports many features, some which may not be found in popular commercial compression software.

For encryption, 7z archives support the 256-bit Rijndael AES cipher. Encryption can be enabled for both files and the 7z directory structure. When the directory structure is encrypted, users are required to supply a password to see the filenames contained within the archive.
7-Zip flexibly supports volumes of dynamically variable sizes, useful for backups on removable media such as writable CDs and DVDs.
When in 2-panel mode, 7-Zip can be considered a basic orthodox file manager.
7-Zip has the ability to unpack archives with corrupted filenames, renaming the files as required.
Lets users make Self-extracting archives so that users who dont have the 7-Zip codec can still extract compressed files.