File extensions & Show All Files

Assuming you're using some version of Microsoft Windows, here is how to turn your file extensions on, and to show all files.  Double-click My Computer, then click on the View (or Tools) menu, and choose "Folder Options".  This should pop up a little window for you.  At the top, there should be a tab called View -- click on that.  Now, there should be some check boxes on that window there.  Look for one that says, "Hide file extensions for known types", and uncheck it.  Then, look for one that says "Show hidden files and folders" and check it.  [Note: depending on which version of Windows you have, the exact wording may be different for the boxes on your View tab.]


Every file on your computer has an extension.  This is the last 3 (or sometimes 4) characters in the filename, and it's purpose is to tell Windows what kind of file it is.  (It also tells you what kind of file it is.)

For example, if you have a picture that you downloaded from the net and saved on your Windows desktop, it might be called "mypic.bmp", where bmp is the file's extension (also known as the the file type: as in "a bmp file").  That stands for bitmap (a type of picture), and Windows knows that when you double-click on a bitmap file, it should use the Paint program (Start, Programs, Accesories, Paint) to open the file.  If you've installed another image editing program, it may have set itself up so that Windows uses it to open bitmap files.

So the idea is that every file has an extension which indicates what kind of file it is (aka, what kind of data it contains).  Windows keeps track of these "associations", as they're called, between file types and the programs that handle those files.  That way, when you double-click on a wav file, Windows knows to call up your sound playing program, instead of, say, Paint... because Paint doesn't understand sound files.  Note that there are many programs available to play sound files (indeed, there are many programs for almost every kind of file), but only one is set as the default player for each type of sound file on any given computer, so only that one will open when you double-click on the file.

Another example: if you download music from my site, you'll need to download and install WinAmp to play it, because the music is stored in files with an mp3 extension (also known as mp3 files).  There is a sound player installed with Windows, and it can play wave (extension: wav) files, midi (mid) files, maybe even CD audio (cda) files.  But it probably can't play MPEG-1 audio layer 3 (mp3) files... you need a player like WinAmp to play them.  The setup program almost always takes care of the extension business for you (or, it may ask you what kind of files you want it to handle).  Using the WinAmp example: when it's installing, it will tell Windows to associate mp3 files with it, so that when you click on a song in mp3 format, WinAmp will open and start playing the file.

If you're saying, "Wait, my files don't have extensions!", don't worry.  Most people can't see their extensions either, and it's just a simple setting to show them.  Technically, your files do have extensions, it's just that Windows is hiding them from you (some people get scared when they see the extensions on their files, and some people change them accidentally and then don't know how to get the file to work again, so Windows has this option).  All you have to do is double-click "My Computer", then click the View menu (or Tools menu), then Folder Options.  Under the "View" tab, look around for a checkbox that says "hide file extensions for known types" and uncheck it. 

There's no reason to have your extensions hidden, because the more you see them, the more you'll understand about the file type and the program used to open the file.  It may seem overwhelming at first, because there are tons of extensions, but you'll get to know the most-used ones very quickly.  Understanding what file extensions are and knowing which ones go with which programs will save you from some very common and frustrating problems that come up in the process of installing software and downloading files from the internet.