What do all these filename extensions mean. Here's a list that explains many of them, together with links to shareware for manipulating or just viewing many of these.
There may be some applications, like viewers, converters etc., shown behind the description; These are usually shareware or freeware for Windows 3.1 or higher. They are written in italic and are shortened. The meaning of these abbreviations can be found on the Shareware List page. The links on this page mostly refer to the homepages of these concerning applications. From there on it should be easy to try to locate a download link.
But what is a filename extension?!
A filename extension is the mostly 3 letter word that you see after the period in a filename. In the Dos/Windows world, extensions are mostly up to three characters. Since Windows 95, extensions can be larger than 3 characters. On a computer running an Unix variant (Linux etc.) filenames can even have more than one extension, all seperated by periods.
Extensions are usefull for determening the type of a file. Is it a text (e.g. extension .txt, .doc)?, an image (e.g. .gif, .jpg) or maybe a sound (e.g. .wav, .mid)?
There must be thousands of extensions. Some are well-known and used very often, others are used just once by a single program. Programmers are free to make up their own extensions.
On this site I try to make an inventory of extensions, sorted in alphabetical order. You might think this site is usefull if you encountered a file somewhere and you don't know what to do with it. There's a good chance it can be found in the list, and if you're lucky there's also a shareware suggested for viewing or converting it. If not, maybe the description will help you to look further.
Some MIME types can be found in the extensions base. MIME stands for 'Multipurpose Internet Mail Extensions', which is a protocol that is used for defining file attachments for the web. This info can also be used for finding the use of an extension.
Though extensions are usefull for determing the type of a file, they are not perfect. For example the '.doc' extension can be used for a simple ASCII text file as well as for various wordprocessing formats. This can be hard for finding a proper viewer for it (or how to associate it in Windows).
It also occurs often that a file has a wrong extension: A filename with the '.jpg' extension could really be a '.gif' or the other way round. Though they're both images, the formats of these files are entirely different. If you try to open such a file in an application that knows both formats, it may leave you behind with an error message like 'The format of this file is unknown, can't read file header' etc. In such a case it may be hard to find out what the real extension should be.
To try to solve such problems, you can check out WhatFormat. This is a file analyser for Ms Windows which can be downloaded from this site. This little util looks at the first bytes of a given file for certain patterns, to try to determine the format of a file. These patterns are often called 'signatures'. I believe in the Unix world, people often speak of 'magic numbers'. Besides looking at signatures, WhatFormat also looks at the filename extensions. It has the same database as this website, that is, the website is updated more often...
I would like to thank everyone who helped adding content to Joz's Extensions Base and WhatFormat :-)