20.02 alpha 2020-08-08
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- The default number of LZMA2 chunks per solid block in 7z archive was increased to 64.
It allows to increase the compression speed for big 7z archives, if there is a big number
of CPU cores and threads.
- The speed of PPMd compressing/decompressing was increased for 7z/ZIP/RAR archives.
- The new -ssp switch. If the switch -ssp is specified, 7-Zip doesn't allow the system
to modify "Last Access Time" property of source files for archiving and hashing operations.
- Some bugs were fixed.
- New localization: Swahili.
Notes about changes in 7-Zip 20.02
The size of solid block for 7z/LZMA2 archives was increased, so 7-Zip can use more threads and chunks to compress solid block. It can improve the compression speed for multi-core processors like Threadripper/Epyc and Xeon. Also it can slightly improve multi-core LZMA2 decompression speed.
Some important parts of PPMd code were rewritten for faster compression and decompression.
And that new PPMd code works faster for data that is not too compressible, like exe files or already compressed data.
Also PPMD in previous 7-Zip could be slow in some Intel CPUs for decompression, if CVE-2018-3639 Speculative Store Bypass (SSB) mitigation was enabled in system. And new PPMd code must work faster for such cases too.
Another change of 7-Zip 20.02 is speed optimization in Delta filter code, that is about two times faster than in previous version.