7z
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| Filename extension | .7z |
|---|---|
| Internet media type | application/x-7z-compressed |
| Uniform Type Identifier (UTI) | org.7-zip.7-zip-archive |
| Magic number | '7', 'z', 0xBC, 0xAF, 0x27, 0x1C |
| Developed by | Igor Pavlov |
| Initial release | 1999 |
| Type of format | Data compression |
| Open format? | Yes: GNU Lesser General Public License |
| Website | 7-zip |
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 License. The LZMA SDK 4.62 was placed in the public domain in December 2008. The latest stable version of 7-Zip and LZMA SDK is version 16.
The 7z file format specification is distributed with 7-Zip's source code. The specification can be found in plain text format in the 'doc' sub-directory of the source code distribution.
The 7z format provides the following main features:
The format's open architecture allows additional future compression methods to be added to the standard.
The following compression methods are currently defined:
A suite of recompression tools called AdvanceCOMP contains a copy of the DEFLATE encoder from the 7-Zip implementation; these utilities can often be used to further compress the size of existing gzip, ZIP, PNG, or MNG files.
The LZMA SDK comes with the BCJ / BCJ2 preprocessor included, so that later stages are able to achieve greater compression: For x86, ARM, PowerPC (PPC), IA-64 Itanium, and ARM Thumb processors, jump targets are normalized before compression by changing relative position into absolute values. For x86, this means that near jumps, calls and conditional jumps (but not short jumps and conditional jumps) are converted from the machine language "jump 1655 bytes backwards" style notation to normalized "jump to address 5554" style notation; all jumps to 5554, perhaps a common subroutine, are thus encoded identically, making them more compressible.
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