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 .

Z: The UNIX compress program is used to reduce the size of a single file. If more than one file is to be compressed, they must be tarred together first. By default the compress program will create a file with the "Z" extension. This file will have to be uncompressed before use and will not be easily uncompressed on non-UNIX systems. It is probably better to use gzip both for reasons of portability and compactness.
z1, z2, z3, z3, z4, z5, z6, z7, z8, & zco: A Z-Machine 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 Z-machine interpreter, and such interpreters are available for virtually every machine in existance (often for free). The 1-4 variants are classic Infocom style; the 5-8 variants are newer. Types 1, 2, 4, 6, and 7 are extremely uncommon; most Z-machine data files are types 3, 5, or 8. Type 8 allows for a much longer, more complex story than the other types -- if types 3 & 5 are viewed as being similar to short stories or novellas, type 8 can be viewed as being as long (or longer) than a full novel. Type 6 provides some graphics support.
zblorb & zlb: A Blorb file designed to work within a Z-Machine.
zcml: Zope Configuration Mark-up Language files are XML files used for the configuration of Zope Web sites.
zip: A file that has been compressed with either the zip or pkzip program will get the "zip" extension. It is similar in portability and performance to gzip (with gzip being perhaps slightly more portable), and similar in performance (but more portable than) sit. Unlike gzip, zip does not require a separate tarring step; it uses its own method to do the equivalent.
zpt & pt: Used for creating dynamic XML, a page template is itself an XML file built around a handful of namespaces including TAL, TALES, METAL, and I18N. Originally used only with Zope, page templates are now being used with several applications.