LZMA vs LZMA2 vs WinRAR64...

[Teddy Rogers]

Had a bit of a slow day today so decided to do a mini-review/test...

With the weather being bad today and having some hours to kill (watching some movies) I decided to check out the new LZMA2 (64-bit) compression which will be included in the up-coming 7-ZIP v9 release. You may ask why version 9 and not 4, I think it is to reference the year it will be released. Please correct me if I am wrong

I also decided to compress the same files using the up-coming release of WinRAR64. It has an improved and updated compression engine to support more modern multi-core and multi-threaded CPU's, instructions and memory. It all sounds promising on paper but can this old yet updated compression algorithm really stand up against its more modern counterpart?

http://www.tuts4you.com/download.php?view.2726

Ted.

[human]

well lzma2 like doc says is worse than lzma, it only compress better uncompressible data. and yet there are compressors that have better compression than lzma, but are a lot slower, use more memory etc.

[Teddy Rogers]

The only instance where compression ratios could be worse is when threads of 4 or more are used because of the way LZMA2 handles the data-stream:

If LZMA2 is set to use only such number of threads required for one chunk, it doesn't split stream to chunks. So you can get different compression ratio for different number of threads. You can get the best compression ratio, when you use 1 or 2 threads.

I found while carrying out various tests LZMA2 always compresses files better than LZMA and definitely always better than WinRAR. Certainly <4 threads produces the best results but you have to compromise over the saved minutes vs the slightly larger files. If time is of important then in my test the extra 25MB gained using greater thread counts is negligible especially when you consider its a whole 17 minutes over a single thread count.

One thing I have noticed is that LZMA2 has better compression ratios with smaller files unlike LZMA which, is now better than WinRAR. LZMA has a good reputation for producing better ratios from bigger file structures over WinRAR whilst WinRAR generally always produced better ratios from smaller files. Now LZMA2 is able to achieve and beat both.

Of course there are better compression engines out there but what makes LZMA and LZMA2 better than those is it is able to achieve great ratios in a much smaller time frame. Having done some tests against other compression engines in the past the time frame vs the ratio result isn't usually worth the effort because in a lot of those tests the ratios were negligible against LZMA. The returns are certainly nothing near as great as what these current test showed against WinRAR.

You could also take in to account LZMA2 now allows for much faster decompression times...

Ted.