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  "markdown": "bzip2, by Julian Seward, compresses with the Burrows–Wheeler transform in independent blocks of 100–900 kB. It beats [gzip](/codecs/data/gzip/) on ratio, particularly for text, but is slow in both directions, single-threaded, and is outperformed on speed, and usually on ratio, by [xz](/codecs/data/xz/) and [zstd](/codecs/data/zstd/). Today it is mainly something you decompress: old source tarballs (`.tar.bz2`) and some datasets. For new files, use zstd or xz.\n\n## Common commands\n\n```sh\nbzip2 -k file              # file.bz2, 900k blocks, keep the original\nbzip2 -1 file              # 100k blocks: faster, less memory, worse ratio\nbzip2 -d file.bz2          # decompress (or bunzip2); bzcat to stdout\nbzip2 -t file.bz2          # test integrity\n```\n\nbzip2 **deletes** the input unless you pass `-k`. The `-1` … `-9` options set the block size to 100 kB … 900 kB; the default is `-9`, and smaller blocks only help when memory is limited. Compression at `-9` needs about 7.6 MB of memory and decompression about 3.7 MB (`-s` reduces it to at most 2.5 MB, at some cost in speed).\n\n## Archives and parallelism\n\n```sh\ntar -cjf backup.tar.bz2 dir/\ntar -xf backup.tar.bz2\n```\n\nThe reference `bzip2` uses a single thread. Because blocks are independent, parallel implementations such as `pbzip2` and `lbzip2` can speed it up and also decompress `.bz2` files in parallel. 7-Zip can also create bzip2 with multiple threads (`7z a -tbzip2`).\n\n## Pitfalls\n\n- **Block independence helps recovery.** Damage to one block loses only that block, and `bzip2recover` can extract the intact ones. gzip has no equivalent.\n- **Poor on binary or already-compressed data** and slower than modern alternatives; the gain over gzip rarely justifies the time.\n- **`.bz2` is a single stream,** not an archive. Combine it with [tar](/codecs/data/tar/) for directories.\n"
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