7-Zip is an open source file archiver designed originally for Microsoft Windows, and later made available to other computer operating systems. In the form of p7zip, 7-Zip has been ported for use on Unix-like systems such as GNU/Linux, BSD, and Mac OS X as well as AmigaOS. 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 the 7z archive format, as well as being able to read several other archive formats. In operation a user can use the command line (all systems), graphical user interface ("Windows" only) or seamless Windows shell environment methods of control.

7-Zip began in 2000 and is actively developed by Igor Pavlov. 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 RAR license restrictions), with the AES code under the revised BSD license, and as such is free software.

7-Zip 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 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 comparatively 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.

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.

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.

It should be noted that the inclusion of some of these formats subjects the package to various terms and conditions that effectively make it non-free. (For example 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.

A 64-bit version is available for x64 Editions of Windows, 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. It is packaged by PortableApps.com and is available from their site.

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. WinZip developed AES encryption standard is also available to encrypt ZIP archives but doesn't offer filenames encryption like 7z.

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 thought of 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 do not have the 7-Zip codec can still extract compressed files.

Notes


SourceForge.net: 7-Zip
7-Zip Portable
AES Encryption Information: Encryption Specification AE-1 and AE-2