Viewing and Changing Windows File Extensions
What is a file extension?
In Microsoft Windows, a file extension tells your computer what type of program to use to open a file. The file extension is a three-letter code that appears at the end of a file name, although it is often hidden (more about that in a minute).
For example, if a file is named mythesis.doc, the .doc is the file extension, and it tells Windows that the file was created with Microsoft Word. If a file is called mythesis.xls, then the extension is .xls and this tells Microsoft Windows that the file was created with Excel.
So, where are these file extensions?
Microsoft Windows will hide all file extensions by default. The idea is that most people won't want to bother with extensions, since changing a file extension can cause trouble (if you change it to the wrong thing) and since Windows mostly takes care of dealing with extensions behind the scenes,
However, there may be times when you want to see file extensions. Perhaps you just like to know what is going on behind the scenes, or perhaps you have a file with the wrong extension and you need to change it.
How do I see file extensions?
Windows XP, 2000, and Me:
- Open My Computer. Go to the Tools menu and select Folder Options.
- Click on the View tab and scroll down to "Hide file extensions for known file types".
- Remove any checkmark next to this option.
- Click OK.
[To hide file extensions, repeat these steps, but this time make sure there is a checkmark.]
Windows 98:
- Open My Computer. Go to the View menu and select Folder Options.
- Click on the View tab and scroll down to "Hide file extensions for known file types".
- Remove any checkmark next to this option.
- Click OK.
- Close the My Computer window.
[To hide file extensions, repeat these steps, but this time make sure there is a checkmark.]
Renaming a file
Now that you can see the full file name, it is possible to rename any part of the file, including the file extension. Be very careful and don't do this unless you have a good reason to. You may want to make a note of the original file extension in case you need to change it back.
- Right-click on the file.
- Click Rename and make your change, then press Enter.
Example: to change mythesis.xlq to mythesis.xls, right-click on mythesis.xlq, click Rename, erase the .xlq and type in .xls (the dot is important) and press Enter. Now the next time you double-click on this file, Windows will attempt to open it using Excel.
To learn more...
You'll find more information on this topic in Windows Help — search for file extension.
An external site that gives more information about file extensions is www.fileinfo.net.