bzip2-1.0.1: description + notes
bzip2 compresses files using the Burrows-Wheeler block-sorting text compression algorithm, and Huffman coding. Compression is generally better than that achieved by more conventional LZ77/LZ78-based compressors, and approaches the performance of the PPM family of statistical compressors. The command-line options are deliberately very similar to those of GNU gzip, but they are not identical.

Compared to gzip -9, bzip2 is slower and gives a slightly better compression. Decompression is significantly slower than gzip. Depending on your case, it may be worth it (or not) to invest the extra time in compressing/decompressing with bzip2 instead of the more standard gzip to gain a small advantage in multiple download times, etc.

The Bzip2 home page has more information.

For the curious, here are some running times and compressed file sizes numbers for comparison. The input data was a 25765100 byte file, comprised of roughly 17.5MB of text and 9.5MB of binary data (a copy of /unix).

command user time size      command user time size
gzip -1 26.770s 12302784 bzip2 -1 120.584s 10408869
gzip -2 27.918s 12085628 bzip2 -2 124.446s 10214448
gzip -3 34.023s 11877150 bzip2 -3 132.282s 10155324
gzip -4 35.784s 11600827 bzip2 -4 142.633s 10116976
gzip -5 43.801s 11410215 bzip2 -5 152.525s 10089397
gzip -6(*) 68.693s 11301849 bzip2 -6 161.633s 10104382
gzip -7 80.467s 11277504 bzip2 -7 171.962s 10070502
gzip -8 131.727s 11248002 bzip2 -8 179.706s 10097078
gzip -9 189.888s 11241577 bzip2 -9(*) 189.888s 10090504
(*) default setting.
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