7-Zip

7-Zip

7-Zip in Windows 7
Developer(s)	Igor Pavlov
Initial release	18 July 1999 (1999-07-18)
Stable release	9.20  (18 November 2010 (2010-11-18)) [±]
Preview release	9.25 alpha  (September 16, 2011 (2011-09-16)) [±]
Written in	C++
Operating system	Microsoft Windows, Linux, Mac OS X
Available in	79 languages, including Brazilian Portuguese, Czech, English, French, German, Italian, Japanese, Polish, Russian, Simplified Chinese, Spanish and Korean
Type	File archiver
License	LGPLv2.1+ with unRAR restriction
Website	www.7-zip.org

7-Zip is an open source file archiver. 7-Zip operates with the 7z archive format, but can read and write several other archive formats. The program can be used from a command line interface, graphical user interface, or with Microsoft Windows shell integration. 7-Zip began in 1999 and is actively developed by Igor Pavlov. It is related to a cross-platform port, p7zip.

7-Zip is free software distributed under the GNU Lesser General Public License (LGPL). It was the winner of the SourceForge.net 2007 community choice awards for "Technical Design" and for "Best Project".

Formats

The 7z archive format

Main article: 7z

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 uses a variety of algorithms, the most common of which are bzip2, LZMA2, 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 GB in size, backed by a range coder.

The native 7z file format is open and modular. All filenames are stored as Unicode.

The official 7z file format specification is distributed with the program's source code. The specification can be found in plain text format in the 'doc' subdirectory of the source code distribution.

Other supported formats

7-Zip supports a number of other compression and non-compression archive formats including:

Packing/unpacking of 7-Zip, ZIP, GZip, bzip2, xz, tar, and, since version 9.20, WIM.

Unpacking only: APM, ARJ, CAB, RAR, MSLZ, EXE, SWF, FLV, SquashFS, CramFS, NTFS, FAT, VHD, MBR, Z, LHA, cpio, smzip, JAR, ISO CD/DVD images (7-Zip version 4.42 and up), DMG, HFS, RPM, onepkg and Debian DEB archives.

According to the 7-Zip website, since version 4.65 (from 2009-02-03), 7-Zip can unpack the following formats in addition to the formats it fully supports: ARJ, CAB, CHM, cpio, DEB, DMG, HFS, ISO, LZH, LZMA, MSI, NSIS, RAR, RPM, UDF, WIM, XAR, and Z.

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. Similarly, some Microsoft executable programs (.EXEs) which are self-extracting archives or otherwise contain archived content (e.g., some setup files) may be opened as archives.

Since the 7-Zip 9.14 beta, 7-Zip can open and view the content of VHD virtual hard disks.

When compressing ZIP or gzip files, 7-Zip uses its own DEFLATE encoder, which is often able to achieve higher compression levels, but at lower speed, than the more common DEFLATE implementation of zlib. The 7-Zip deflate encoder implementation is available separately as part of the AdvanceCOMP suite of tools.

Variants

In the form of p7zip, the command line version has been ported for use on Unix-like systems including Linux, FreeBSD, Mac OS X and AmigaOS 4. J7Z is a GUI front end for p7zip, which runs on Windows and Linux under Java SE. A GUI front end for p7zip on the Mac OS X operating system named keka is also available.

Two command line versions are provided: 7z.exe, using external libraries; and a standalone 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 repackaged version for Windows is available by PortableApps.com.

Features

7-Zip supports:

• 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. WinZip-developed zip file AES encryption standard is also available in 7-Zip to encrypt ZIP archives with AES 256-bit, but it does not offer filename encryption as in 7z archives.
• Volumes of dynamically variable sizes, allowing use for backups on removable media such as writable CDs and DVDs.
• Usability as a basic orthodox file manager when used in 2-panel mode.
• Multiple-core CPU threading settings can be configured.
• The ability to attempt to open EXE files as archives, allowing the decompression of data from inside many "Setup" or "Installer" or "Extract" type programs without having to launch them.
• The ability to unpack archives with corrupted filenames, renaming the files as required.
• The ability to create self-extracting single- (but not multi-) volume archives.
• Command line interface.

Reception

Snapfiles.com gave 7-zip 4.5 stars out of 5, noting that its "interface and additional features are fairly basic, but the compression ratio is outstanding." On Tech Republic, Justin James found the detailed settings for Windows File Manager integration were "appreciated," and called the compression/decompression benchmark utility "neat". And though the comprehensive archive dialog has settings that "will confuse most users,", he concluded, "7-Zip fits a nice niche in between the built-in Windows capabilities and the features of the paid products, and it is able to handle a large variety of file formats in the process." The 2011 review of version 9.20 in PC World magazine pointed out that 7-Zip can "compress and e-mail files in one easy step", and although it offers "options that most users should never have to think about ... The default settings are just fine."

See also

• Comparison of file archivers
• FreeArc

External links

• Official website
• SourceForge.net: 7-Zip
• 7-Zip .NET wrapper
• 7-Zip Portable at PortableApps.com
• 7-Zip Theme Manager