5.2 Learn to love Windows file extensions File extensions are much more important in Windows than in Unix. In UNIX the file extensions are a matter of convenience, while in Windows the three-letter extension identifies what type of file it is, or determines which application owns a file. For example, you might like to call your plain text files .doc for document, but in Windows that file will automatically be opened with Microsoft Word, because that's the default for that extension. There are cases where the operating system or application program can become confused if you have the wrong file type. Avoid trouble by using the expected extension.
Registry is where extensions are matched up with applications.
File appears with correct icon and opens by double-clicking if the registry can match the suffix with the right application. But at times, Windows 2000 is just different enough from Unix to be annoying. The systems group has set up the TAB key as the way to complete commands on the login nodes. Using F7 to pop up the history list does not change the list. Most of the Unix commands listed above actually do work on the login nodes.