7-Zip

7-Zip is a free compression program, which is licensed under the terms of the LGPL. The development is carried out by the Russian programmer Igor Viktorovich Pavlov, the first version of 7 -Zip in 1999 published and actively developed to date (November 2013). 7-Zip is the reference implementation of the Lempel -Ziv - Markov algorithm developed by him ( LZMA ) dar. 7-Zip has been awarded as the best SourceForge open source project in July 2007.

  • 2.1 LZMA
  • 2.2 encryption
  • 3.1 Embedding in Microsoft Windows

Formats

The 7z archive format

By default, generated 7-Zip archives in 7z format with the file extension .7 for Each archive can contain many directories and files. In 7z is basically a pure container format, constructed open and modular. Thus security and data compression functions to be implemented by a series of cascaded filters. This then implement as preprocessors compression algorithms or encryption filter.

All file names are stored in Unicode encoding.

Other supported formats

7-Zip also supports a range of compressed and non- compressed archive formats:

Packing and Unpacking

The following formats can be both either bought or unpacked:

  • Bzip2 (. bz2 )
  • Gzip (. gz),
  • Tar (. tar),
  • Zip ( including AES encryption with 256 bit Rijndael. zip )
  • Xz (including LZMA2. xz ),
  • Wim (. wim ).

For compression of zip and gzip files using 7-Zip a Deflate encoder self-developed, often better results than the Deflate implementation much more frequently used by zlib, but this comes at the expense of compression speed. This version of Deflate encoder is also independent of 7-Zip available as part of advancecomp suite.

Just unpack

In addition, archive contents or packed data from files of the following formats can be extracted:

General-purpose archives
  • ARJ (. Arj )
  • Cpio (. cpio. io )
  • LHArc (. Lzh. Lha )
  • RAR (. Rar )
Program archives

7-Zip can open some Windows Installer (. Msi) and provides access to the entire contents, including a meta - files. Also can be personalized with LZX compressed Microsoft cabinet files (. Cab) and compressed with LZMA Nullsoft Scriptable Install System Installation open programs. The same applies (eg extension. Exe) for some other executable programs.

Therefore, 7-Zip also be used to check if it is an archive with an unknown binary file and extract its contents if necessary.

File system images
  • Apple disk image (. Dmg)
  • Apple Hierarchical File System
  • Microsoft's Virtual Hard Disk (. Vhd )
  • VMWare Virtual Machine Disk (. Vmdk )
Multimedia files
  • Flash Video (. Flv)
  • Smzip ( Stepmania games files)
  • Shockwave Flash (. Swf)
Compressed individual files
  • Compress (. Z)
  • Raw LZMA data streams (. lzma )
  • MSLZ
Other
  • Compiled HTML Help (. Chm)
  • Windows program files (resources and other components look and unzip )
  • Unix split / cat ( joining of fragmented files)

Unsupported

The ACE format is not supported due to licensing reasons.

Algorithms

The native 7z compression makes use of a variety of algorithms. After sorting the files to be packaged in a convenient order and ( in progressive compression) of any chain to a continuous data stream certain types of files with different pre-filters or preprocessors can be refined to achieve better results in the subsequent compression. To this end, appropriate filters as BCJ and BCJ2 be used for Windows program files x86 machine code for executables supported in a number of formats. The decorrelation of, for example PCM and raster graphics data is a delta - filter.

For the following main compression step, the method LZMA, PPMd and bzip2 are supported when native 7z format.

Then an encryption step with AES can be followed.

With the LZMA and pre-filters used in default predominantly better compression rates than other common formats can be achieved. Especially for large amounts of data it outperforms the widely used RAR often significantly.

LZMA

LZMA is a relatively new, self-developed by Igor Pavlov and imported with 7-Zip method. It uses an improved variant of the LZ77 algorithm, Markov chains and a Bereichskodierer ( an implementation of arithmetic coding ) for entropy coding.

Encoding

7-Zip supports the standardized AES 256 -bit Rijndael encryption. Encryption can be enabled separately for both the compressed files as well as for the 7z directory structure. If the directory structure is encrypted, you must have the correct password be entered to display the names of files in the archive.

The WinZip AES encryption standard is also supported, so that ZIP archives can be encrypted with 256 bit AES. However, no encryption of the directory structure as in 7z archives is possible.

Functions

7-Zip has many features, including:

  • The possibility of storing the compressed and archived data held in a single archive in several sections ( volumes) with fixed or dynamically variable size. This makes it easy to create backup files on removable media such as CD- RW or DVD -writable.
  • Exact settings to use multiple processors / cores / threads.
  • The ability to unpack archives with corrupted file name information, the files are renamed if necessary.
  • The possibility tentatively executable files (. Exe) to open as an archive. Thus, data from many installers and self-extracting archives can be unpacked without the appropriate program must be running.
  • Self-extracting archives can be created. This only works for archives in a file, not for archives with multiple volumes.
  • In 2- panel mode, the program can also be used as a simple " orthodox " File Manager ( in the style of Norton Commander for example ).

Embedding in Microsoft Windows

The graphical user interface is seamlessly integrated via "drag and drop " and context menu in Microsoft Windows a. A command line version and a plugin for FAR Manager are included.

Availability for different operating systems

7-Zip is designed for Microsoft Windows, but it exists with p7zip also a portable command-line version of the program, which can be cross-platform compiled for the BSDs, Linux, Unix, OS / 2, BeOS and AmigaOS 4.

There are many frontends for p7zip, which allow, for example, integration into graphical user interfaces.

Furthermore, there is the XZ Utils a collection of tools based on the LZMA code of LZMA SDK to pure data compression (ie without archiving function), with which the LZMA similar to programs such as gzip, bzip2 or zlib ( for example, in combination with tar) can be exploited.

7zX is an implementation for Mac OS X that but with the version for Windows only the compression format in common. The application itself is built on a separate code base.

There are Java, . NET and Python bindings.

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