Understanding File Types

The term File Types describes the collection of associations between documents and the applications that use them. The most apparent use of this feature is that, for example, Windows knows to run Notepad when you double-click on a file with the .txt extension. The traditional method for configuring these associations to suit your needs is discussed in Section 4.2.2 in Chapter 4, but it goes quite a bit deeper than that.

It all starts with file extensions, the letters (usually three) that follow the period in most filenames. For example, the extension of the file Readme.txt is .txt, signifying a plain text file; the extension of Resume.wpd is .wpd, signifying a document created in WordPerfect. By default, Windows hides the extensions of registered file types in Explorer and on the desktop, but it’s best to have them displayed.

File extensions not only allow you to easily determine what kind of file a certain file is (because icons are almost never descriptive enough), but also allow you to change Windows’ perception of the type of a file by simply renaming the extension. Note that changing a file’s extension doesn’t actually change the contents or the format of the file, only how Windows interacts with it.

To display your file extensions, select Folder Options in Explorer’s Tools menu, choose the View tab, and turn off the Hide file extensions for known file-types option. Click OK when you’re done.

By hiding file extensions, Microsoft hoped to make Windows ...

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