Glossary of Computer File Extensions

Filename Extensions List

So you see a file somewhere on the 'net with a name like "" 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 TADS (Text Adventure Development System) data file. Typically it will represent an interactive fiction story (or interactive tutorial, or similar). It is binary but will work on any machine with some flavor of TADS interpreter, and such interpreters are available for several different platforms, usually for free. It is currently not as portable as a Z-machine file.
gblorb & glb
A Blorb file designed to work within a Glulx virtual machine.
A GEOS dictionary file. It is (obviously) meant to be used with GEOS.
This file is used for holding genealogy data, and is most typically called a GedCom file (short for genealogy data communications). Most software applications made for performing genealogy work (or even just basic family trees) are capable of working with GedCom files and they can generally be used on all platforms. Note however that some companies have made proprietary extensions to the GedCom format, so transfers from one software application to another are not completely guaranteed to be safe.
A GeoWorks document; it can be used on any machine with GeoWorks installed (which in turn requires GEOS).
The Generic Font format is used to store font information. It will work on any machine that has TEX installed.
A general image format file is a representation of an image or simple animation. The format was created by Compuserve and is copyrighted. It is currently the most widely accepted image format in existence, but the concern over its copyright has inspired many people to try and move away from its use. Some popular alternatives include JPEGs, PNGs, and X-bitmaps for still images and MPEGs and QuickTime movies for animations. A GIF can only contain two-hundred fifty-six different colors, of which "transparent" is an allowed color. Each GIF can use its own set of 256 colors, though.
An OmniGraffle file is a type of XML format. It is used to hold charts and diagrams.
gz & z
The GNU Zip program is used to compress the size of a single file. If more than one file has to be compressed, they must be tarred together first. The program that does the compression is called gzip, and the gzipped file cannot be used until it has been gunzipped. The gzip program has its origins on UNIX machines, but it has been ported to most other computer types as well and is typically available for free under the terms of the GNU public license. The "gz" form is preferred; the other is considered obsolete as it was frequently confused with the output of the UNIX compress program and deliberately changed to be something more distinctive. Gzip is better at compression than compress.