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 .

The C64 tape file stores the contents of an entire C64 tape in a single file. It is binary, but is designed to work on any machine that has C64 emulator software (C64 emulators are available for many platforms, including UNIX, Macs, and WinTel boxes) as well as (of course) the C64 (or C128) itself.
Groups of files are often tarred together so that they may be handled as a single file. A file that ends with this extension is probably such a file and will have to be untarred into its individual components before use. The whole concept of tarring started on UNIX machines, but it is also possible to get programs to tar and untar on most other computers.
A file with this extension is typically a program written in the Tcl programming language. It should be in simple ASCII and should be usable on any machine with Tcl/Tk.
template & tem
A template file written in the C++ programming language. It should be in simple ASCII and (depending upon how portably it was written) should be usable on any machine with a C++ compiler. A template file will typically also require some C and h files to be used in any meaningful way.
The TEX Font Metric file is used to provide information on TEX fonts. It is binary, but will work on any machine that has TEX installed.
The Targa image format can read by numerous different image manipulation programs for several different platforms. It is frequently used in special effects and raytracing work.
It is so common to tar a batch of files and then compress them with gzip that the result is often given the "tgz" extension instead of "tar" and "gz" in sequence.
thtml & ttml
Very similar to shtml but utilizes Tcl to do its work.
tiff & tif
The tagged image file format is a lossless format for storing image data. TIFF is a popular output format for scanners and other similar devices. Free viewers exist for TIFFs on most platforms, but most browsers lack direct TIFF support.
This is a simple ASCII file used by the TopicCrunch program (available only on MS-Windows) to store keywords plus domain and search engine settings to allow re-running search engine optimization checks.
A TomeRaider e-book file. It is binary and not particularly portable; it can currently only be used with Palm Pilots, Psions, Windows '98, and some flavors of Windows CE. It is currently not supported on any other type of PDA or OS.
This file type is used to exchange data between numerous spreadsheet and database applications. It is in simple ASCII (in fact, it is just a collection of tab-separated values) and is platform-neutral.
The Truetype Font format is used for storing vector fonts. It originated on Macintoshes and WinTel boxes and can be made to work on many other systems as well. Unfortunately there are two slightly different Truetype formats in use; modern Macintoshes can use either, WinTel boxes are restricted to the WinTel type, and other systems can sometimes use either but will usually be restricted to one or the other. Free conversion programs exist to convert between the two.
txt & text
This is a generic sort of extension indicating a simple text file (usually ASCII). It can be readily used on virtually any computer, although sometimes character set differences will require slight conversions. A file with this extension will not typically have significant formatting; that would decrease its simplicity and portability.
This is a generic sort of extension indicating some sort of "type" data; of particular note though is that native Amiga font files often use this extension.