7z
In computing, 7z is an archive format which allows data compression using a number of compression algorithms. The format was initially implemented by the 7-Zip archiver but the file format is public and 7-Zip's implementation of it is publicly available under the GNU LGPL licence. The main features of the 7z format are: Open, modular architecture (which allows any compression, conversion, or encryption method to be used)High compression ratio (depending on which compression method is used)Strong AES-256 encryption Support for large files (up to approximately 16 exabytes)Unicode file namesCompression of archive headersAllows compact archives: As with e.g. RAR and TGZ, one compressed data stream contains several files, as opposed to e.g. ZIP, where the archive file contains a separate compressed data stream for each archived file. The format's open architecture allows additional compression methods to be added to the standard. The following are defined in the current version: LZMA - Improved and optimized version of LZ77 algorithm, using Markov chains/entropy coding and Patricia tries.PPMD - Dmitry Shkarin's 2002 PPMdH (PPMII/cPPMII) with small changes: PPMII is an improved version of the 1984 PPM compression algorithm (prediction by partial matching).BCJ - Converter for 32-bit x86 executables, see LZMA. Compresses target addresses of near jumps and calls.BCJ2 - Converter for 32-bit x86 executables, see LZMA. Jump, call and conditional jump targets addresses are compressed separately.Bzip2 - Standard Burrows-Wheeler transform algorithm. Bzip2 uses (faster) Huffman coding, while Bzip is using (stronger) entropy coding.DEFLATE - Standard LZ77-based algorithm 7z also supports encryption with the AES algorithm with a 256-bit key. The key is generated from a user-supplied passphrase using an algorithm based on the SHA-256 hash algorithm (with a large number of iterations, to make a brute-force search for the passphrase more difficult). The MIME type of 7z is application/x-7z-compressed. Other compressors which use PPMII: RAR Compressors which encode branch targets to improve program file compression ratio: UPX - for x86 16- and 32-bit binaries. 7-Zip - for x86 32-bit binaries, ARM, ARMThumb, PPC and IA64. RAR - for x86 32-bit and for IA64 Itanium. Also has preprocessors for true color data, audio data and tables.
See also List of archive formats
External links 7-Zip homepage 7-Zip for Unix Dimtry Shkarin (Institute for Dynamics of Geospheres, Moscow, Russia) 2002: PPM: One Step to Practicality
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