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7z Format
7z is a new archive format, providing a very high compression ratio.
The main features of 7z format:
- Open architecture
- High compression ratio
- Strong AES-256 encryption
- Ability to use any compression, conversion or encryption method
- Supports files with sizes up to 16000000000 GB
- Unicode file names
- Solid compression
- Archive header compression
7z has an open architecture, so it can support any new compression method, too. The following methods currently are integrated into 7z:
| Method | Description |
|---|---|
| LZMA | Improved and optimized version of LZ77 algorithm |
| PPMD | Dmitry Shkarin's PPMdH with small changes |
| BCJ | Converter for 32-bit x86 executables |
| BCJ2 | Converter for 32-bit x86 executables |
| BZip2 | Standard BWT algorithm |
| Deflate | Standard LZ77-based algorithm |
LZMA is the default and general compression method of 7z format. The main features of LZMA are:
- High compression ratio
- Variable dictionary size (up to 4 GB)
- Compression speed: about 1 MB/s on 2 GHz CPU
- Decompression speed: about 10-20 MB/s on 2 GHz CPU
- Small memory requirement for decompression (depend from dictionary size)
- Small code size for decompression: about 5 KB
- Supports multi-threading and P4's hyper-threading
The LZMA compression algorithm is very suitable for embedded applications. LZMA is released under the terms of the GNU LGPL. LZMA is also available under a proprietary license for those who can not use the GNU LGPL in their code. If you want to use the LZMA source code, you can request consultations, custom code programming, or the required developer licenses at the support page: Send message to LZMA developer. You also may wish to check the information about the LZMA SDK.
7-Zip supports encryption with the AES-256 algorithm. This algorithm uses a cipher key with a length of 256 bits. To create that key, 7-Zip runs a derivation function based on a SHA-256 hash algorithm. A key derivation function produces a derived key from the text password entered by the user. To increase the cost of an exhaustive search to crack a password, 7-Zip uses a large number of iterations when it produces a cipher key from a password.
7z is part of the 7-Zip program distributed under the GNU LGPL. You can download 7-Zip source and various binaries from the Download Page.
Applications that support 7z archives include WinRAR, PowerArchiver, TUGZip, and IZArc.
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Copyright (C) 2008 Igor Pavlov.