Format
The 7z format
7z is the new archive format 7-Zip is built around, providing a high compression ratio through an open, pluggable architecture rather than one fixed algorithm.
Main features
Open architecture
New compression, conversion, and encryption methods can be plugged in without breaking the format.
High compression ratio
The default method, LZMA, is tuned specifically for this — see the LZMA SDK page for the numbers.
Strong AES-256 encryption
A 256-bit cipher key derived from your password via a SHA-256-based function, run through a large number of iterations to resist brute-forcing.
Very large files
Supports files and archives up to 16,000,000,000 GB, with Unicode file names throughout.
Solid compression
Groups files together before compressing, which improves ratio further, plus compressed archive headers.
Any method, mixed
An archive can combine compression, conversion, and encryption methods rather than being locked to one.
Methods and filters currently integrated
Compression methods
LZMALZMA2PPMdBZip2Copy
PPMd is Dmitry Shkarin's PPMdH, with small changes.
Filters
- BCJ / BCJ2
- ARM64 / ARMT / ARM
- PPC / SPARC / IA64
- Delta
- Swap2 / Swap4
The executable converters improve ratio on compiled binaries; Delta helps on WAV-like data.
Who else reads 7z
7z code is part of 7-Zip, distributed under the GNU LGPL, and most of it is also included in the LZMA SDK. Beyond 7-Zip itself, WinRAR, PowerArchiver, TUGZip, IZArc all support opening 7z archives.
See the real spec on 7-zip.org/7z.html.