Windows XP for Starters: The Missing Manual: Exactly What You Need to Get Started

5.9. Filename Extensions

Every operating system needs a mechanism to associate documents with the applications that created them. When you double-click a Microsoft Word document icon, for example, Word launches and opens the document.

In Windows , every document comes complete with a normally invisible filename extension (or just file extension )a period followed by a suffix that's usually three letters long. Here are some common examples:

Table 5-1.

5.9.1. Displaying Filename Extensions

It's possible to live a long and happy life without knowing much about these extensions. Indeed, because file extensions don't feel very user -friendly, Microsoft designed Windows to hide the suffixes on most icons (see Figure 5-7). If you're new to Windows, and haven't poked around inside the folders on your hard drive much, you may never even have seen them.

Some people appreciate the way Windows hides the extensions, because the screen becomes less cluttered and less technical-looking. Others make a good argument for the Windows 3.1 days, when every icon appeared with its suffix.

For example, in a single Desktop window, suppose one day you discover that three icons all seem to have exactly the same name : PieThrower. Only by making filename extensions appear would you discover the answer to the mystery: that is, one of them might be called PieThrower.ini, another is an Internet-based software updater called PieThrower.upd, and the third is the actual PieThrower program, PieThrower.exe.

One way to make sense of such situations is simply to look at the window in Details view (right-click in the window and choose View Details from the shortcut menu).

But that's too easy. To fully breathe in Windows technology, you can instruct Windows to reveal the file suffixes on all icons. To do so, choose Tools Folder Options from any folder windows menu bar. In the Folder Options dialog box, click the View tab. Turn off "Hide extensions for known file types," and then click OK: the filename extensions for all icons appear.