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:
|When you double-click this icon||this program opens it|
|Fishing trip.doc||Microsoft Word|
|Quarterly results.xls||Microsoft Excel|
|Home page.htm||Internet Explorer|
|A home movie.avi||Windows Media Player|
For an exhaustive list of every file extension on the planet, visit http://whatis.com; click the link for “Every File Format in the World.”
Behind the scenes, Windows maintains a massive table that lists every extension and the program that “owns” it. To see this list, choose Tools→Folder Options from the menu bar of any folder window. When the Folder Options box appears, simply click the File Types tab (Figure 5-8).
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 5-9). 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.
Figure 5-8. Each ...