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.
A home movie.avi
Windows Media Player
For an exhaustive list of every file extension in the world, visit www.whatis.com; click the link for “Every file extension 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.
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 10-10). If you’re new to Windows, you may never have even 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 ...