7-Zip
Encyclopedia
7-Zip is an open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

 file archiver
File archiver
A file archiver is a computer program that combines a number of files together into one archive file, or a series of archive files, for easier transportation or storage...

. 7-Zip operates with the 7z
7z
7z is a compressed archive file format that supports several different data compression, encryption and pre-processing algorithms. The 7z format initially appeared as implemented by the 7-Zip archiver. The 7-Zip program is publicly available under the terms of the GNU Lesser General Public...

 archive format, but can read and write several other archive formats. The program can be used from a command line interface, graphical user interface
Graphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...

, or with Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 shell integration. 7-Zip began in 1999 and is actively developed by Igor Pavlov
Igor Pavlov (programmer)
Igor Pavlov is a Russian freelance programmer and is the creator and the maintainer of the file archiver 7-Zip and its toolset. He is also the creator of the 7z archive format...

. It is related to a cross-platform
Cross-platform
In computing, cross-platform, or multi-platform, is an attribute conferred to computer software or computing methods and concepts that are implemented and inter-operate on multiple computer platforms...

 port, p7zip
P7zip
p7zip is a port of the command line version of the 7-Zip file archiver to POSIX-conforming operating systems, such as Unix, Linux, FreeBSD, Windows NT and Mac OS X. It is free software, available under the GNU Lesser General Public License....

.

7-Zip is free software
Free software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

 distributed under the GNU Lesser General Public License
GNU Lesser General Public License
The GNU Lesser General Public License or LGPL is a free software license published by the Free Software Foundation . It was designed as a compromise between the strong-copyleft GNU General Public License or GPL and permissive licenses such as the BSD licenses and the MIT License...

 (LGPL). It was the winner of the SourceForge.net
SourceForge.net
SourceForge is a web-based source code repository. It acts as a centralized location for software developers to control and manage open source software development. The website runs a version of SourceForge Enterprise Edition, forked from the last open-source version available...

 2007 community choice awards for "Technical Design" and for "Best Project".

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 uses a variety of algorithms, the most common of which are bzip2
Bzip2
bzip2 is a free and open source implementation of the Burrows–Wheeler algorithm. It is developed and maintained by Julian Seward. Seward made the first public release of bzip2, version 0.15, in July 1996.-Compression efficiency:...

, 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
Range encoding
Range encoding is a data compression method defined by G. Nigel N. Martin in a 1979 paper Range encoding is a form of arithmetic coding that was historically of interest for avoiding some patents on particular later-developed arithmetic coding techniques...

.

The native 7z file format is open and modular. All filenames are stored as Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

.

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
ZIP (file format)
Zip is a file format used for data compression and archiving. A zip file contains one or more files that have been compressed, to reduce file size, or stored as is...

, tar
Tar (file format)
In computing, tar is both a file format and the name of a program used to handle such files...

, and, since version 9.20, WIM.

Unpacking only: APM
Apple Partition Map
Apple Partition Map is a partition scheme used to define the low-level organization of data on disks formatted for use with 68K and PowerPC Macintosh computers that was introduced with the Macintosh SE ....

, ARJ
ARJ
ARJ is a software tool designed by Robert K. Jung for creating high-efficiency compressed file archives. ARJ is currently on version 2.85 for DOS and 3.15 for Windows and supports 16-bit and 32-bit Intel architectures.ARJ was one of two mainstream archivers for DOS and Windows during early and...

, CAB
Cabinet (file format)
In computing, CAB is the Microsoft Windows native compressed archive format. It supports compression and digital signing, and is used in a variety of Microsoft installation engines: Setup API, Device Installer, AdvPack and Windows Installer.Though Cabinet was originally called Diamond, its .CAB...

, RAR, MSLZ, EXE
EXE
EXE is the common filename extension denoting an executable file in the DOS, OpenVMS, Microsoft Windows, Symbian, and OS/2 operating systems....

, SWF
SWF
SWF is an Adobe Flash file format used for multimedia, vector graphics and ActionScript. Originating with FutureWave Software, then transferred to Macromedia, and then coming under the control of Adobe, SWF files can contain animations or applets of varying degrees of interactivity and function.,...

, FLV, SquashFS
SquashFS
SquashFS is a compressed read-only file system for Linux. SquashFS compresses files, inodes and directories, and supports block sizes up to 1 MB for greater compression...

, CramFS
Cramfs
The compressed ROM file system is a free read-only Linux file system designed for simplicity and space-efficiency. It is mainly used in embedded systems and small-footprint systems....

, NTFS
NTFS
NTFS is the standard file system of Windows NT, including its later versions Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7....

, FAT
File Allocation Table
File Allocation Table is a computer file system architecture now widely used on many computer systems and most memory cards, such as those used with digital cameras. FAT file systems are commonly found on floppy disks, flash memory cards, digital cameras, and many other portable devices because of...

, VHD, MBR
Master boot record
A master boot record is a type of boot sector popularized by the IBM Personal Computer. It consists of a sequence of 512 bytes located at the first sector of a data storage device such as a hard disk...

, Z
Compress
Compress is a UNIX compression program based on the LZC compression method, which is an LZW implementation using variable size pointers as in LZ78.- Description of program :Files compressed by compress are typically given the extension .Z...

, LHA
LHA (file format)
LHA is a freeware compression utility and associated file format. It was created in 1988 by , and originally named LHarc. A complete rewrite of LHarc, tentatively named LHx, was eventually released as LH. It was then renamed to LHA to avoid conflicting with the then-new MS-DOS 5.0 LH command...

, cpio
Cpio
cpio is a general file archiver utility and its associated file format. It is primarily installed on Unix-like computer operating systems. The software utility was originally intended as a tape archiving program as part of the Programmer's Workbench , and has been a component of virtually every...

, smzip, JAR
JAR (file format)
In software, JAR is an archive file format typically used to aggregate many Java class files and associated metadata and resources into one file to distribute application software or libraries on the Java platform.JAR files are built on the ZIP file format and have the .jar file extension...

, ISO
ISO image
An ISO image is an archive file of an optical disc, composed of the data contents of every written sector of an optical disc, including the optical disc file system...

 CD/DVD images (7-Zip version 4.42 and up), DMG
Apple Disk Image
Apple Disk Image is a proprietary disk image format commonly used with the Mac OS X operating system. The format allows secure password protection as well as file compression and hence serves both security and file distribution functions; it is most commonly used to distribute software over the...

, HFS
Hierarchical File System
Hierarchical File System is a file system developed by Apple Inc. for use in computer systems running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs...

, RPM
RPM Package Manager
RPM Package Manager is a package management system. The name RPM variously refers to the .rpm file format, files in this format, software packaged in such files, and the package manager itself...

, onepkg and Debian DEB
Deb (file format)
deb is the extension of the Debian software package format and the most often used name for such binary packages. Like the "Deb" part of the term Debian, it originates from the name of Debra, erstwhile girlfriend and now ex-wife of Debian's founder Ian Murdock.Debian packages are also used in...

 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
ARJ
ARJ is a software tool designed by Robert K. Jung for creating high-efficiency compressed file archives. ARJ is currently on version 2.85 for DOS and 3.15 for Windows and supports 16-bit and 32-bit Intel architectures.ARJ was one of two mainstream archivers for DOS and Windows during early and...

, CAB
Cabinet (file format)
In computing, CAB is the Microsoft Windows native compressed archive format. It supports compression and digital signing, and is used in a variety of Microsoft installation engines: Setup API, Device Installer, AdvPack and Windows Installer.Though Cabinet was originally called Diamond, its .CAB...

, CHM, cpio
Cpio
cpio is a general file archiver utility and its associated file format. It is primarily installed on Unix-like computer operating systems. The software utility was originally intended as a tape archiving program as part of the Programmer's Workbench , and has been a component of virtually every...

, DEB
Deb (file format)
deb is the extension of the Debian software package format and the most often used name for such binary packages. Like the "Deb" part of the term Debian, it originates from the name of Debra, erstwhile girlfriend and now ex-wife of Debian's founder Ian Murdock.Debian packages are also used in...

, DMG
Apple Disk Image
Apple Disk Image is a proprietary disk image format commonly used with the Mac OS X operating system. The format allows secure password protection as well as file compression and hence serves both security and file distribution functions; it is most commonly used to distribute software over the...

, HFS
Hierarchical File System
Hierarchical File System is a file system developed by Apple Inc. for use in computer systems running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs...

, ISO
ISO image
An ISO image is an archive file of an optical disc, composed of the data contents of every written sector of an optical disc, including the optical disc file system...

, LZH
LHA (file format)
LHA is a freeware compression utility and associated file format. It was created in 1988 by , and originally named LHarc. A complete rewrite of LHarc, tentatively named LHx, was eventually released as LH. It was then renamed to LHA to avoid conflicting with the then-new MS-DOS 5.0 LH command...

, LZMA, MSI
Windows Installer
The Windows Installer is a software component used for the installation, maintenance, and removal of software on modern Microsoft Windows systems...

, NSIS
Nullsoft Scriptable Install System
Nullsoft Scriptable Install System is a script-driven Windows installation system with minimal overhead backed by Nullsoft, the creators of Winamp...

, RAR, RPM
RPM Package Manager
RPM Package Manager is a package management system. The name RPM variously refers to the .rpm file format, files in this format, software packaged in such files, and the package manager itself...

, UDF
Universal Disk Format
Universal Disk Format is an implementation of the specification known as ISO/IEC 13346 and ECMA-167 and is an open vendor-neutral file system for computer data storage for a broad range of media. In practice, it has been most widely used for DVDs and newer optical disc formats, supplanting ISO 9660...

, WIM, XAR
Xar (archiver)
Xar is an open source file archiver and the archiver’s file format. It was created within the OpenDarwin project and is used in Mac OS X 10.5 for software installation routines, as well as browser extensions in Safari 5.0...

, and Z
Compress
Compress is a UNIX compression program based on the LZC compression method, which is an LZW implementation using variable size pointers as in LZ78.- Description of program :Files compressed by compress are typically given the extension .Z...

.

7-Zip is able to open some MSI
Windows Installer
The Windows Installer is a software component used for the installation, maintenance, and removal of software on modern Microsoft Windows systems...

 files, allowing access to the meta-files within along with the main contents. Some Microsoft CAB (LZX
LZX (algorithm)
LZX is the name of an LZ77 family compression algorithm. It is also the name of a file archiver with the same name. Both were invented by Jonathan Forbes and Tomi Poutanen.-Amiga LZX:...

 compression) and NSIS
Nullsoft Scriptable Install System
Nullsoft Scriptable Install System is a script-driven Windows installation system with minimal overhead backed by Nullsoft, the creators of Winamp...

 (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
VHD (file format)
A Virtual Hard Disk is a virtual hard disk file format, meaning it can contain what is found on a physical hard disk drive, such as disk partitions and a file system, which in turn can contain files and folders. It is typically used as the hard disk of a virtual machine...

.

When compressing ZIP or gzip files, 7-Zip uses its own DEFLATE
DEFLATE
Deflate is a lossless data compression algorithm that uses a combination of the LZ77 algorithm and Huffman coding. It was originally defined by Phil Katz for version 2 of his PKZIP archiving tool and was later specified in RFC 1951....

 encoder, which is often able to achieve higher compression levels, but at lower speed, than the more common DEFLATE implementation of zlib
Zlib
zlib is a software library used for data compression. zlib was written by Jean-Loup Gailly and Mark Adler and is an abstraction of the DEFLATE compression algorithm used in their gzip file compression program. Zlib is also a crucial component of many software platforms including Linux, Mac OS X,...

. The 7-Zip deflate encoder implementation is available separately as part of the AdvanceCOMP
AdvanceCOMP
AdvanceCOMP is a set of cross-platform command line data compression tools. The utilities allow modifying an already-compressed file, with the intent of reducing the file-size by optimising the compressed representation...

 suite of tools.

Variants

In the form of p7zip
P7zip
p7zip is a port of the command line version of the 7-Zip file archiver to POSIX-conforming operating systems, such as Unix, Linux, FreeBSD, Windows NT and Mac OS X. It is free software, available under the GNU Lesser General Public License....

, the command line version has been ported for use on Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....

 systems including Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

, FreeBSD
FreeBSD
FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...

, Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 and AmigaOS 4
AmigaOS 4
AmigaOS 4, , is a line of Amiga operating systems which runs on PowerPC microprocessors. It is mainly based on AmigaOS 3.1 source code, and partially on version 3.9 developed by Haage & Partner...

. J7Z is a GUI front end for p7zip, which runs on Windows and Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 under Java SE. A GUI front end for p7zip on the Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 operating system named keka
Keka
Keka is a Mac OS X frontend GUI of p7zip, the UNIX port of 7-Zip. It allows users to compress files and folders into files that are usually of a smaller size that can be extracted afterwards for use again. 7-Zip, using the .7z format, is a very high compression format that in many cases beats ZIP...

 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
7z
7z is a compressed archive file format that supports several different data compression, encryption and pre-processing algorithms. The 7z format initially appeared as implemented by the 7-Zip archiver. The 7-Zip program is publicly available under the terms of the GNU Lesser General Public...

, ZIP
ZIP (file format)
Zip is a file format used for data compression and archiving. A zip file contains one or more files that have been compressed, to reduce file size, or stored as is...

, gzip
Gzip
Gzip is any of several software applications used for file compression and decompression. The term usually refers to the GNU Project's implementation, "gzip" standing for GNU zip. It is based on the DEFLATE algorithm, which is a combination of Lempel-Ziv and Huffman coding...

, bzip2
Bzip2
bzip2 is a free and open source implementation of the Burrows–Wheeler algorithm. It is developed and maintained by Julian Seward. Seward made the first public release of bzip2, version 0.15, in July 1996.-Compression efficiency:...

, Z
Compress
Compress is a UNIX compression program based on the LZC compression method, which is an LZW implementation using variable size pointers as in LZ78.- Description of program :Files compressed by compress are typically given the extension .Z...

 and tar
Tar (file format)
In computing, tar is both a file format and the name of a program used to handle such files...

 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
PortableApps.com
PortableApps.com is a site offering portable software for Windows.The site was founded by John T. Haller and includes contributions from over 100 people, including developers, designers and translators.-History:...

.

Features

7-Zip supports:
  • The 256-bit AES
    Advanced Encryption Standard
    Advanced Encryption Standard is a specification for the encryption of electronic data. It has been adopted by the U.S. government and is now used worldwide. It supersedes DES...

     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
    Password
    A password is a secret word or string of characters that is used for authentication, to prove identity or gain access to a resource . The password should be kept secret from those not allowed access....

     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
    Volume (compression)
    A volume is a term in data compression for a file that has been compressed and split into different parts.There are many advantages in having a compression utility with the ability for compression into volumes. First, it allows an individual to download the file in segments at his or her own pace...

     of dynamically variable sizes, allowing use for backups on removable media such as writable CDs
    Compact Disc
    The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...

     and DVD
    DVD
    A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

    s.
  • 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
    Self-extracting archive
    A self-extracting archive is a computer application which contains a file archive, as well as programming to extract this information. Such file archives do not require a second executable file or program to extract from the archive, as archive files usually require...

    .
  • Command line interface.

Limitations

While 7-Zip supports file sizes of up to 16 exabytes, it has an unusually high overhead allocating memory for files, on top of the memory requirements for performing the actual compression.

Approximately 1 kilobyte is required per file, more if the pathname is very long; the file listing alone can grow to an order of magnitude greater than the memory required to do the actual compression. In real world terms, this means 32-bit systems cannot compress more than a million or so files in one archive, as the memory requirements exceed the 2 GB process limit.

64-bit systems do not suffer from the same process size limitation, but still require several gigabytes of RAM to overcome this limitation. Archives created on such systems could not be opened on machines with less memory.

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
PC World (magazine)
PC World is a global computer magazine published monthly by IDG. It offers advice on various aspects of PCs and related items, the Internet, and other personal-technology products and services...

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."

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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