7-Zip

Infobox Software

developer = Igor Pavlov
released = 2000
frequently_updated = yes
programming language = C++, C
operating system = Microsoft Windows
language = 69 languages, including Brazilian Portuguese, Czech, English, French, Italian, Japanese, Simplified Chinese and Spanish
genre = File archiver
license = GNU Lesser General Public License
GNU Lesser General Public License with unRAR restriction [http://www.7-zip.org/license.txt 7-Zip License for use and distribution] ]
website = http://www.7-zip.org/

7-Zip is a free software/open source file archiver designed originally for Microsoft Windows. In the form of p7zip, the command-line version of 7-Zip has been ported to Unix-like systems such as GNU/Linux, BSD, Mac OS X and AmigaOS. It can be made compatible with DOS by using the HX-DOS extender to run the Windows command-line version.

7-Zip operates primarily with the 7z archive format, as well as being able to read and write to several other archive formats. In operation a user can use the command line, graphical user interface or Windows shell integration. 7-Zip began in 2000 and is actively developed by Igor Pavlov. It is related to a cross-platform port, p7zip.

In contrast to the market-leading programs WinZip and WinRAR, which remain as proprietary competitors, 7-Zip is distributed under the terms of the GNU Lesser General Public License (LGPL) (with the unRAR license restrictions), and as such is free software (excluding the non-free RAR code). 7-Zip was the winner of the SourceForge.net 2007 community choice awards for "Technical Design" and for "Best Project". [http://sourceforge.net/projects/sevenzip SourceForge.net: 7-Zip] ]

Formats

The 7z archive format

By default, 7-Zip creates 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 4 GiB in size, backed by a range coder.

LZMA compression ratios tend to be very efficient. 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. All filenames are stored as Unicode.

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, smzip, JAR, rpm and Debian deb archives. Versions of 7-Zip from 4.42 onwards also support ISO CD/DVD images.

It should be noted that the inclusion of one of these formats subjects the package to various terms and conditions that effectively make it non-free (the inclusion of the proprietary RAR code.)

7-Zip is able to open some 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 more common DEFLATE implementation of zlib, at the expense of compression speed. The 7-Zip deflate encoder implementation is available separately as part of the AdvanceCOMP suite of tools.

Variations

In the form of p7zip, the command line version has been ported for use on Unix-like systems including Linux, FreeBSD and Mac OS X. There are several GUI frontends for p7zip such as Q7Z. An alternate GUI for 7-Zip on Windows, #7Z, has been released by the same developers. [ [http://k7z.sourceforge.net/ Homepage of the Q7Z and #7Z GUI frontends] ]

Two command line versions are provided: 7z.exe, using external libraries; and a stand-alone executable 7za.exe containing built-in modules. However, 7za's compression/decompression support is limited to 7z, ZIP, gzip, bzip2, Z and tar formats. A 64-bit version is available for 64-bit editions of Windows, with support for large memory maps leading to faster compression. All versions support multi-threading.

A freeware application based on the 7-Zip engine, [http://www.jzip.com/ jZip] , is available for Microsoft Windows. Its stated focus is an easier, more streamlined user interface than 7-Zip.

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 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, unless only the data was encrypted but not the filenames. WinZip-developed AES encryption standard is also available to encrypt ZIP archives but doesn't offer filename encryption like 7z. [ [http://www.winzip.com/aes_info.htm AES Encryption Information: Encryption Specification AE-1 and AE-2] ]
* 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.
* 7-Zip has the ability to create self-extracting archives.

ee also

*Comparison of file archivers

Notes

External links

* [http://www.7-zip.org/ 7-Zip] 7-Zip Home
* [http://sourceforge.net/projects/sevenzip/ SourceForge.net: 7-Zip]