B1 (archive format)

B1 is an open archive file format that supports data compression and archiving.[1] B1 files use the file extension ".b1" or ".B1" and the MIME media type application/x-b1. B1 incorporates the LZMA compression algorithm.[2] 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.[3] B1 files are created and opened with its native open-source B1 Pack Tool, as well as B1 Free Archiver utility.[4][5]

Filename extension.b1
Internet media typeapplication/x-b1
Developed byCatalina Group Ltd
Initial release2011
Type of formatData compression

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.[6] B1 Pack Project is released under the Apache License.[7] 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.[8]

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.[9]

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

External links

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