bzip2 dictionary size

[Wladmir]

Is there any way to use the bzip2 compression in 7zip with dictionary size greater than 900kb?

[Piotr Tarsa]

No.

BZip2 format has 9 sizes of blocks to choose, biggest one is 900 KB. Compression can only be improved using some preprocessors like Srep.

[joerg]

@Piotr_Tarsa

you are right for the original bzip2 1.0.5

but for pbzip2 (parallel bzip2)
from http://compression.ca/pbzip2/
(fully compatible with the original bzip2)

it is possible to set a blocksize bigger then 900k

Usage: pbzip2 [-1 .. -9] [-b#cdfhkp#qrtVz] <filename> <filename2> <filenameN>
-b# : where # is the file block size in 100k (default 9 = 900k)

the effect we can see at the following graf

http://compression.ca/pbzip2/bench-itanium2.gif

you can see also http://encode.dreamhosters.com/showthread.php?t=253

best regards

[Piotr Tarsa]

I think that with only small changes to BZip2 source code one can release a version with any block size. But official BZip2 supports only 100 KB - 900 KB blocks.