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BZ2, BZzip2 compressed archive file (.bz2)

The BZ2 Archive file format

BZ2 files refer to the free and open source file compression bzip2 program files. This program uses the Burrows-Wheeler algorithm to compress single files, as opposed to a file archiver. This form of data compression is more efficient and effective than older methods (Z, ZIP, GZ, etc) but it is a slower process. Conversion is accomplished by taking data in blocks (100-900 kB in size) and using the Burrows-Wheeler transformation to convert characters which occur regularly into strings of identical letters, then applying “move-to-front” transformation and Huffman coding. The earlier BZIP used arithmetic coding. Decompression of these files is generally quick.

Technical details of BZ2 files

Different layers of compression are used and stacked in the process of creating BZ2 files. Run-length encoding replaces sequences of 4-255 consecutive duplicate symbols. Burrows-Wheeler transformation is a reversible block-sort transformation. Blocks are self-contained with an operating limit of 900 kB. Move to front transformation does not alter the size of processed blocks. Symbols are processed and replaced by location and moved to the front. Repeating symbols are replaced. Run length encoding replaces long strings of repeated symbols by combining a symbol and sequence of two special codes (RUNA, RUNB), decreasing repeated symbols with codes and the number of repeated symbols. Huffman coding replaces fixed length symbols based on frequency of use, shortening sequences used regularly throughout the code. Huffman tables, Unary base 1 encoding, Delta encoding, and Sparse bit array are also used.

More information about the BZ2 file format

File extension .bz2
File category Archive
Example file Download example.tar.bz2 file
Associated programs Corel WinZip
Smith Micro StuffIt Deluxe 2010
WinRAR 5
PeaZipExternal Link
7-Zip
Incredible Bee Archiver
The Unarchiver
Useful links More information on BZ2
File conversion Convert a file to BZ2
Developer Julian Seward
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