7-Zip

From Encoresoup - The Ultimate Guide to Free/Open Source Software

7-Zip is a free software/open source file archiver designed originally for Microsoft Windows. 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".^[2]

Contents 1 Formats 1.1 The 7z archive format 1.2 Other supported formats 2 Variations 3 Features 4 See also 5 Notes 6 External links

[edit] Formats

[edit] 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 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.

[edit] 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.

[edit] 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.^[3]

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, jZip, is available for Microsoft Windows. Its stated focus is an easier, more streamlined user interface than 7-Zip.

[edit] 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.^[4]
• 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.

[edit] See also

• Comparison of file archivers

[edit] Notes

[edit] External links

• 7-Zip 7-Zip Home
• SourceForge.net: 7-Zip

v • d • e Data compression software implementations
Video codecs (Comparison)	MPEG-4 ASP 3ivx · DivX · Nero Digital · FFmpeg MPEG-4 · HDX4 · Xvid H.264/MPEG-4 AVC CoreAVC · Nero Digital AVC  · QuickTime H.264 · x264 Lossless CorePNG · FFV1 · Huffyuv · Lagarith · MSU Lossless Others Cinepak · Sorenson · Dirac · Indeo · VP3 · VP7 · Pixlet · RTVideo  · Snow · Tarkin · Theora · WMV · SIF1
Audio codecs (Comparison)	General ADPCM · ATRAC · Dolby Digital · DTS · Musepack · TwinVQ · Vorbis · WMA Speech/Voice iLBC · IMBE · iSAC · QCELP · RTAudio  · Siren · Speex · Truespeech Lossless Apple Lossless · Dolby TrueHD · DTS-HD Master Audio · FLAC · Monkey's Audio · OptimFROG · TTA · WavPack · WMA Lossless
Archivers (Comparison)	Open Source 7-Zip · Ark · File Roller · Info-ZIP · KGB Archiver · PeaZip · The Unarchiver Freeware 7zX · DGCA · Filzip · GCA · IZArc · StuffIt Expander · TUGZip · Zipeg · ZipGenius · WinUHA Proprietary ALZip · Archive Utility · MacBinary · PowerArchiver · Squeez · StuffIt · WinAce · WinRAR · WinRK · WinZip Command line ARC · ARJ · JAR · bzip2 · compress · gzip · Info-ZIP · LHA · lzop · PAQ · PKZIP · RAR · SBC · UPX
See Compression Methods for methods and Compression Formats and Standards for formats

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