7-Zip is a free and open-source file archiver, a utility used to place groups of files within compressed containers known as «archives». It is developed by Igor Pavlov and was first released in 1999.7-Zip uses its own 7z archive format, but can read and write several other archive formats. The program can be used from a command-line interface as the command p7zip,or through a graphical user interface that also features shell integration. Most of the 7-Zip source code is under the GNU LGPL license; the unRAR code, however, is under the GNU LGPL with an «unRAR restriction», which states that developers are not permitted to use the code to reverse-engineer the RAR compression algorithm.
Main article: 7z (file 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
7-Zip supports a number of other compression and non-compression archive formats (both for packing and unpacking), including ZIP, Gzip, bzip2, xz, tar and WIM. The utility also supports unpacking APM, ARJ, CHM, cpio, DEB, FLV, JAR, LHA/LZH, LZMA, MSLZ, Office Open XML, onepkg, RAR, RPM, smzip, SWF, XAR and Z archives and CramFS, DMG, FAT, HFS, ISO, MBR, NTFS, SquashFS, UDF and VHD disk images. 7-Zip supports the ZIPX format for unpacking only. It has had this support since at least version 9.20, which was released in late 2010.