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:

7z at Wikipedia