Windows Vista Annoyances

Filename Extensions and File Associations

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.

Table 6-1 shows some common examples.

Table 6-1. Filename Extensions

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
Agenda.wpd	Corel WordPerfect
A home movie.avi	Windows Media Player
Sudoku.gadget	Sidebar gadget
Animation.dir	Macromedia Director

Tip

For an exhaustive list of every file extension on the planet, visit http://www.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. More on this in a moment.

Displaying Filename Extensions

It’s possible to live a long and happy life without knowing much about these extensions. Because file extensions don’t feel very user-friendly, Microsoft designed Windows to hide the suffixes on most icons (Figure 6-7). If you’re new to Windows, you may never have even seen them.

Figure 6-7. As a rule, Windows shows filename ...