The ZIP file format is a data compression and archive format. A ZIP file contains one or more files that have been compressed to reduce file size, or stored as-is. The ZIP file format permits a number of compression algorithms, but as of 2009[update], the Deflate method continues to be dominant.
bzip2’s ancestor bzip used arithmetic coding after the block sort. This was discontinued because of a software patent restriction and was replaced by the Huffman coding currently used in bzip2.[4]
bzip2 is known to be quite slow at compressing, leading users to opt for alternatives such as gzip when time is an issue. This problem is asymmetric, as decompression is relatively fast. Motivated by the large CPU time required for compression, a modified version was created in 2003 that supported multi-threading, giving significant speed improvements on multi-CPU and multi-core computers. As of January 2008[update], this functionality has not been incorporated into the main project.
