7-Z

Default file extension for 7z compressed archive file is 7z.

7z is the new backup, archive - compressed file format, providing high compression ratio.

The main features of 7z format:
- Open architecture
- High compression ratio
- Strong AES-256 encryption
- Ability of using any compression, conversion or encryption method
- Support for very large files with sizes up to 16000000000 GB
- Unicode file name support
- Solid compression ratio
- Archive headers compression

7z has an open architecture, so it can support any new compression method, too. The following methods currently are integrated into 7z:

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.

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.