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7z Format
7z is the new archive 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
- Supporting files with sizes up to 16000000000 GB
- Unicode file names
- Solid compressing
- Archive headers compressing
7z has open architecture, so it can support any new compression methods. Now the following compression methods are integrated to 7z:
| Method | Description |
|---|---|
| LZMA | Improved and optimized version of LZ77 algorithm |
| LZMA2 | Improved version of LZMA |
| PPMD | Dmitry Shkarin's PPMdH with small changes |
| BZip2 | Standard BWT algorithm |
| Copy | No compression method |
7z also supports filters that improve compression ratio of main compression method. Now the following filters are integrated to 7z:
| BCJ | Converter for x86 executables |
| BCJ2 | Converter for x86 executables |
| ARM64 | Converter for ARM64 executables |
| ARMT | Converter for 32-bit ARM-Thumb executables |
| ARM | Converter for 32-bit ARM32 executables |
| PPC | Converter for PowerPC executables |
| SPARC | Converter for SPARC executables |
| IA64 | Converter for IA-64 (Itanium) executables |
| Delta | Converter for WAV files |
| Swap2/Swap4 | Converters for changing the order of bytes |
LZMA is default and general compression method of 7z format. The main features of LZMA method:
- High compression ratio
- Variable dictionary size (up to 4 GB)
- Compressing speed: about 2-8 MB/s on 4 GHz CPU (2 cpu threads version).
- Decompressing speed: about 30-100 MB/s on 4 GHz CPU (1 cpu thread).
- Small memory requirements for decompressing (depend from dictionary size)
- Small code size for decompressing: about 5 KB
7-Zip also supports encryption with AES-256 algorithm. This algorithm uses cipher key with length of 256 bits. To create that key 7-Zip uses derivation function based on SHA-256 hash algorithm. A key derivation function produces a derived key from text password defined by user. For increasing the cost of exhaustive search for passwords 7-Zip uses big number of iterations to produce cipher key from text password.
7z code is a part of 7-Zip program distributed under the GNU LGPL. You can download 7-Zip sources and binaries from Download Page.
Major part of 7z code is included to LZMA SDK.
Applications that support 7z archives: WinRAR, PowerArchiver, TUGZip, IZArc.
Links:
Copyright (C) 2023 Igor Pavlov.