Probably a lot of it is due to hardware changes since zlib was first written. Mainly the importance of cache and branch prediction, which were either less of a

Probably a lot of it is due to hardware changes since zlib was first written. Mainly the importance of cache and branch prediction, which were either less of a big deal or non-existent back then. IOW, zlib probably leaves a lot more on the table now than when it was written.