BSDIFF File

What are BSDIFF files and how to open them

Are you having problems opening a BSDIFF file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your BSDIFF files.

What is a BSDIFF file?

A .BSDIFF file is a Bsdiff Patch file.

Bsdiff Patch files store compact differences between two binary versions of a file so that one version can be updated into the other without shipping the entire new file. They are created by the bsdiff tool (developed by Colin Percival) when comparing an "old" file to a "new" file and are applied using the companion tool bspatch.

The format encodes three types of data streams: control instructions, which describe how to reconstruct the new file using matched portions from the old file; diff data, which captures per-byte differences in matched regions; and extra data, which carries raw bytes that exist in the new file but not in the old. These streams are compressed (traditionally with bzip2) to reduce patch size. The patch file begins with a header giving a format signature, the sizes of the compressed control and diff streams, and the size of the output (new version) file.

Files are read by bspatch (or other compatible patching tools) which take the old file plus the patch and produce the new file. Creation is done by bsdiff, which analyzes the old and new files to identify matching regions, computes the diff and extra bytes, and writes out the patch. The tool requires memory proportional to several times the size of the old file.

The internal identifier signature is "BSDIFF40" (in ASCII) at offset 0. Byte patterns characteristic of the format include that signature, and further bytes at offset 27 show "BZh91AY", indicating the use of bzip2 compression in one of the streams.

How to open BSDIFF files

Important: Different programs may use files with the BSDIFF file extension for different purposes, so unless you are sure which format your BSDIFF file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: August 25, 2026

Help us help others

File.org helps thousands of users every day, and we would love to hear from you if you have additional information about BSDIFF file formats, example files, or compatible programs. Please use the links below or email us at submit@file.org to discuss further.