File extension
.bz2
Bzip 2 archives
.bz2 files are bzip2-compressed streams: a block-sorting compressor based on the Burrows-Wheeler transform that usually achieves higher ratios than gzip at the cost of speed.
Known meanings
Formats and reference material for .bz2
Bzip 2 archives
Bzip 2 archives
Details
Format notes
bzip2
bzip2 is a lossless compressor that typically compresses better than gzip,
particularly on text, at the cost of slower operation and higher memory use. A
.bz2 file holds a single compressed stream and, like gzip, is not itself an
archiver, so it is commonly paired with tar to produce .tar.bz2 archives.
Streams begin with the magic bytes BZh followed by a digit giving the block
size.
Rather than the LZ77 dictionary approach used by gzip, bzip2 works in blocks and applies a pipeline of reversible transforms: the Burrows-Wheeler transform to group similar byte sequences, a move-to-front transform, run-length encoding, and finally Huffman coding. Because it operates on independent blocks, a bzip2 stream can be partially recovered around a corrupted block, and parallel implementations can compress or decompress blocks concurrently.
Status And Preservation Notes
bzip2 is stable and widely available, though newer compressors such as xz and
zstd often offer better ratio-versus-speed trade-offs, so bzip2’s use in new
pipelines has declined. The common media type is application/x-bzip2. For
preservation it remains a reasonable, openly documented choice; keep the
original stream and verify integrity on decompression.
Security Notes
As with any compressor, decompressing untrusted .bz2 data can expand to far
more than the stored size, so extractors should bound output size and memory to
resist decompression bombs.
Further Reading
- bzip2 project and documentation:
https://sourceware.org/bzip2/