B1 (archive format)

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Short description: Open archive file format
Filename extension.b1
Internet media typeapplication/x-b1
Developed byCatalina Group Ltd
Initial release2011
Type of formatData compression

B1 is an open archive file format that supports data compression and archiving. B1 files use the file extension ".b1" or ".B1" and the MIME media type application/x-b1. B1 incorporates the LZMA compression algorithm.[1] B1 archive combines a number of files and folders into one or more volumes, optionally adding compression and encryption. Construction of the B1 archive involves creating a binary stream of records and building volumes of that stream. The B1 archive format supports password-based AES-256 encryption.[2] B1 files are created and opened with its native open-source B1 Pack Tool, as well as B1 Free Archiver utility.[3][4]

B1 Pack Project

B1 Pack is an open-source software project that produces a cross-platform command-line tool and a Java library for creating and extracting file archives in the B1 archive format. Source code of the project is published at GitHub.[5] B1 Pack Project is released under the Apache License.[6] The B1 Pack Tool module builds a single executable JAR file which can create, list, and extract B1 archive files from a command-line interface.[7]

B1 format features

  • Support for Unicode names for files inside an archive.
  • Archives and the files inside it can be of any size.
  • Support for split archives, that consist of several parts.
  • Integrity check with the Adler-32 algorithm.
  • Data compression using the LZMA algorithm.
  • Supports encryption with the AES algorithm.[8]

API features

  • Instant creation of an archive without reading from/writing to a file system.
  • Producing only a byte range of an archive, e.g. for resuming downloads.
  • Streaming archive content without prior knowledge of all the files being packaged.


  1. "B1 File Format" Whatis.com. Retrieved 13 January 2014.
  2. "B1 file extension - B1 compressed archive" File-Extensions.org. Retrieved 13 January 2014.
  3. "B1 File Extension" Fileinfo. Retrieved 14 January 2014.
  4. "Extract compressed files without any software" Digital Quest. Retrieved 13 January 2014.
  5. "B1-Pack" GitHub. Retrieved 13 January 2014.
  6. "The Apache Software License, v2.0" Retrieved 14 January 2014.
  7. "B1 Pack CLI" Retrieved 13 January 2014.
  8. "B1 Pack Project" Retrieved 14 January 2014.

External links