BZ2
BZ2 (bzip2) is a single-file compression format, which is slightly slower but slightly more efficient than ZIP's standard 
Deflate compression.
It is optionally used by 
Source 1 FastDL servers to reduce network bandwidth usage, by sending the compressed file, which is then decompressed by the client. This does not reduce storage usage, however; while the FastDL server only needs the BZ2 version, the server needs both the decompressed and BZ2 version, and the client will only keep the decompressed version.
Typical filesizes for BZ2 compression are as such:
- Significant savings: large text files, model files, textures, and uncompressed BSPs
- Marginal savings: WAV files
- Negligible savings: MP3s and LZMA-compressed BSPs
Using BZ2 when savings are small may be undesirable, as this increases load times for clients.
