Saugus.net: Glossary of Computer File Extensions

Filename Extensions List

So you see a file somewhere on the 'net with a name like "greatfile.xyz" and you would like to download it and use it on your computer. Will it work? What does the file extension xyz mean, anyway? This handy guide attempts to provide answers to those questions.

It is not meant to be read straight through; rather, it is meant to be a reference. An extension may be looked up either with the "find in page" option of your browser or by appending a "#xyz" (without the quotes and with xyz replaced by the extension in question) to the "go to" or "URL" field on your browser. There is also a Search Interface that will return not only the specific extension sought but also other entries that reference it. Be aware though that it assumes familiarity with the computer basics discussed on the terms page.

You may notice that most extensions are three letters (or fewer) long. This is due to a historical limitation of the operating system called CP/M (that was later inherited by MS-DOS). In fact, the whole concept of file extensions comes from CP/M. Most modern operating systems do not attribute any special meaning to the "." (period, or dot) character.

Be aware though that there is no standardization to filename extension usage, and many different people have used extensions to apply to many different things. This list only attempts to provide likely guesses of what something is apt to be. Programs that can make use of many of these extensions can be found on the Guide to Free Software.

If you want something added or see a problem with something already here (but keep in mind this guide is not meant to be overly technical) please send .

a: An archived library of object files that can be used in the process of building programs. The generic extension lib is also sometimes used this way.
abw: An AbiWord word processing document; it can be read on any machine with AbiWord installed (available for WinTel boxes, Mac OS X, BeOS, and most UNIXes for free).
adf: The Amiga disk file stores the contents of an entire Amiga floppy in a single file. It is binary, but is designed to work on any machine that has Amiga emulator software (Amiga emulators are available for many platforms, including UNIX, Macs, and WinTel boxes) as well as (of course) the Amiga itself.
afm: The Adobe Font Metric file is used to provide information on Adobe fonts. It is in simple ASCII.
ai: An Adobe Illustrator document. It is binary but will work directly on any machine that has Adobe Illustrator.
aiff & aif: The audio interchange file format originated on Macs but has since been ported to several other platforms as well.
apd: An Aldus PageMaker document. It is binary but will work directly on any machine that has Aldus PageMaker.
arc & ark: A file that has been compressed with the arc program or similar will get the "arc" (and very rarely the "ark") extension. Its performance is somewhat less than gzip & zip, but decompression programs exist on virtually every platform. Like zip, arc does not require a separate tarring step; it uses its own method to do the equivalent.
arj: Similar in all respects to arc, but a different method of compression was used. Programs to uncompress this type of file do not exist on as many platforms as they do for the original arc.
art: An image format (typically called the Johnson-Grace format) with extremely aggressive compression at the expense of quality. This format is most frequently seen by AOL users as AOL automatically compresses online images of other formats (like gif or jpeg) into Johnson-Grace images. This is why AOL users often do not see web pages at the same quality level as other people, often seeing blurry images where others see clear images (and occasionally even seeing black bars that are not really present in images).
asp: A proprietary solution that performs more or less like shtml.
au: An audio format that originated on UNIX systems but has since been ported to virtually every other platform out there from the Newton on up. Note though that these files can be either stereo or mono; stereo is not supported on as many machines as mono.
avi: A video file will typically store a movie clip. It's generally supported by many different platforms, although note that there are several different versions of AVI files in use, and not all players will play all versions.
awk: Probably an AWK script; it can be made to run on any machine that has awk.