PowerArchiver - 7-Zip Compression

7-Zip Compression
and comparison of compression formats in PowerArchiver

Introduction

7-Zip is a new compression format featured in PowerArchiver 2004. It is an open source format, providing open architecture and high compression ratio. It is also an modern format, that supports UNICODE filenames (so international users will not have an issues with special characters), maximum file sizes up to 16000000000 GB, and strong encryption (AES 256 bit). However, 7-Zip's greatest strength is that it is an open format - it is not forcefully controlled by any organization or individual, but an LGPL project that anyone can contribute to. Everyone can find and use latest DLLs and implement them into their application. This way it is impossible have a situation similar to ZIP, where we have several different versions of ZIP files that not everyone can open in the same way, or such as with RAR, which is still not supported by some compression utilities due to its propertiary format. By its nature, everyone is encouraged to use 7-Zip in their applications with fairly liberal LGPL licensing.

Compression ratio

While most users will not understand nor care about what license a format distributed under, they will certainly care about the compression ratio that 7-Zip provides. 7-Zip mostly uses the LZMA compression method found in other formats, but with stronger compression settings and dictionary sizes which result in better (if slower) compression. 7-Zip also uses solid compression which enables a better compression ratio (same as with CAB and RAR). We have tested all formats found in PowerArchiver 2004, as well as some other most popular formats that people use (RAR and ACE) in order to demonstrate compression strengths of 7-Zip.

Compression example
For our example of 7-Zip compression, we have compressed a Championship Manager 03/04 installation, which is a popular game in Europe. We have used a game installation because it is easy to show differences in compression ratios, but if you use any application you will notice similar results.

Notes

Game installation in its original state is 504 MB in size and contains over 2,900 files.
7-Zip at Ultra settings had 15% better compression ratio than WinRar at its highest setting and 39% better compression ratio than Zip at its standard settings. You should see even an better compression ratio as the size of the files that you are compressing goes up, or less as it goes down (but even with smaller files, you should save 10% compared to RAR at its maximum settings).
7-Zip compression is at its best when used to compress applications (binary data), although it is still good for text compression.
ZIP compression - while 7-Zip in this case provides 39% better compression than ZIP, we still recommend use of the ZIP format for most daily tasks, since its speed/compression ratio is still the best.

Things to know about 7-Zip (and its shortcomings)

Because 7-Zip is a relatively new compression format, it still does not have support for multivolumes, editing files inside of solid archives and recovery support, all of which are already planned for next versions of 7-Zip.
Due to its strong compression settings, 7-Zip at Ultra setting will take up a large amount of memory - 369 MB (34 MB for decompression)! However, if you use 7-Zip Maximum compression setting, memory usage will go down to 84 MB (10 MB for decompression) and if you use Normal setting, 7-Zip will use 27 MB of your memory and need only 4 MB for decompression.

PowerArchiver's 7-Zip limitations

Currently, PowerArchiver does not support several features already found in 7-Zip: AES encryption (both read and write), SFX creation (extraction works fine), and detection of solid archives (which is why we can not update files inside 7-Zip archives). We plan to add these and other new 7-Zip features that become available in future PowerArchiver releases.

Find out more about 7-Zip

7-Zip has been created by Igor Pavlov and is distributed under the LGPL. You can find out more about the 7-Zip format here.
You can contribute to the 7-Zip open source project at Source Forge's 7-Zip project page.