xdelta is a command line program for delta encoding

Delta encoding

Delta encoding is a way of storing or transmitting data in the form of differences between sequential data rather than complete files; more generally this is known as data differencing...

, which generates two file difference. This is similar to diff

Diff

In computing, diff is a file comparison utility that outputs the differences between two files. It is typically used to show the changes between one version of a file and a former version of the same file. Diff displays the changes made per line for text files. Modern implementations also...

 and patch

Patch (Unix)

patch is a Unix program that updates text files according to instructions contained in a separate file, called a patch file. The patch file is a text file that consists of a list of differences and is produced by running the related diff program with the original and updated file as arguments...

, but it is targeted for binary files and does not generate human readable output.

It is first released in 1997. It is based on the algorithm of rsync

Rsync

rsync is a software application and network protocol for Unix-like and Windows systems which synchronizes files and directories from one location to another while minimizing data transfer using delta encoding when appropriate. An important feature of rsync not found in most similar...

, which is developed by Andrew Tridgell. The developer of xdelta is Joshua MacDonald and currently maintained by him.

Recent xdelta3 has some unique functions. It can generate standardized VCDIFF

VCDIFF

VCDIFF is a format and an algorithm for delta encoding, described in RFC 3284. The algorithm is based on Jon Bentley and Douglas McIlroy's paper "Data Compression Using Long Common Strings" written in 1999. VCDIFF is used as one of the delta encoding algorithm in "Delta encoding in HTTP" .- Delta...

 format, and it realized the compatibility among other delta encoding software which supports VCDIFF format. It runs on Unix-like

Unix-like

A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....

 operating systems and Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

. xdelta can handle up to 2⁶⁴ bytes files in any platform, and it is suitable for large scale backup.

External links

• Official homepage
• Andrew Tridgell's PHD on rsync, with a section on xdelta
• RFC 3284, The VCDIFF Generic Differencing and Compression Data