FileName.ext : the delimiter is the (last) dot
FileName.EXT : the extension is EXT
The extension defines the file "type", eg text file, executable file, database file or graphic file or .... Actually a remnant from old DOS 8.3 filename limits, it has proven its usefullness over the years and today even normaly "extension-free" systems like UNIX use more and more extensions. An extension lets not only the user easily find out what sort of file it is, but even the OS (or other programs) can easily associate certain file-extensions with certain programs, thus eg starting a certain application when the user clicks on a certain (data-)file.
Thats the theory. In practice it shows that the combinations out of 3 letters are limited and thus there are ambiguities. Since there are absolutely no further investigations done by the OS what concerns the file-type, misunderstandings can happen. Indeed they happen more and more, the more identical extensions are used by different programs. Although today there is no more need to reduce the extension to 3 characters, it seems most programmers stick to it.
So even unexperienced users should be aware of the fact that a .doc file - from a friend, out of the net - needs not necessarily be a Word document, that dll's aren't limited to the dll-extension (Microsoft themselves in their ultimate wisdom breaks this rule often), that some extensions are used by ten different programs(with differing content well understood!).
So if you got a file with an unknown extension or with a well known extension that the associated program can't understand, this extension list can be a first hint what sort of file it may be. If the here listed program too can't open your file, further investigation is necessary. There are automatic file-recognition programs in the net, but their capabilities are limited. Most of them use only the extension to find out what the file actually is. Experienced users will use "dump" or "list" to find out what sort of program it is (for dump or list see soon the new converter page here ). But a lot of knowledge and skill is necessary to find out in this way what the file actually is. Further information on file formats can be found on e.g. www.wotsit.org (very special information normaly thought only for programmers).
Associating File Extensions under
To associate a file extension with an application:
Note: You cannot duplicate an extension already registered.
You can change a previously registered file type (but not the extension) by highlighting its description and clicking the Edit button. If you wish to change the extension, you must delete that extension first, then create the new extension as described above.
Associating Multiple Registered File Extensions
You can associate multiple extensions with one file type by doing the following:
If you couldn't find the extension you searched:
the list is permanently enhanced, revisit this site in a month or so.
More info on file types, Mac file types, Unix file types
Select Extension by starting letter:
A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U -
V - W - X - Y - Z - OTHER - Allowed chars in Filenames
If you find an extension missing, write! No
guaratee given for completeness or correctness. If you feel an
extension is outdated, write!
Authors and retailers: it is in the interest of us all and our customers to avoid the double use of extensions! Please help us keep this compilation up to date!
Send extension data to: firstname.lastname@example.org
Compilation Copyright (c) R.Cooper-Bitsch, visit: also: www.sunorbit.net