Display file extensions in Mac OS X Finder or Windows Explorer

File extensions are important and useful. These are the characters that follow the final period in the file name. They are usually 3 or 4 characters long. They tell an operating system whether or not a file is an application, like Excel.exe, or the file’s associated application. The EXE extension tells Windows that the file is a program. The Mac parallel is APP. Microsoft Word documents use extensions like DOC, DOCX, or DOT. This informs the computer that they are opened with Word.

File extensions are hidden by default on new computers. I guess the smart people at Apple and Microsoft think these important bits of information will confuse a computer user like you. I disagree. They inform us about our files. Since computers have hundreds of thousands or millions of files this extra information helps us navigate.

So how do you show extensions?

Apple OS X Finder

1. Open a Finder window.
2. Click on the Finder —> Preferences… on the menu bar.
3. The Finder Preferences dialog should open.
4. Select the Advanced tab.
5. Check the checkbox Show all filename extensions.
6. Close the dialog window.

Windows Explorer (XP)

1. Open a Windows Explorer window such as My Documents.
2. Click on the menu items Tools —> Folder Options…
3. The Folder Options dialog should open.
4. Select the View tab.
5. Uncheck the Hide extensions for known file types checkbox.
6. Click the OK button to close the dialog.

Windows Explorer (Windows 7 and Vista)

1. Open a Windows Explorer window such as Documents.
2. Click on the menu items Organize —> Folder and Search Options…
3. The Folder Options dialog should open.
4. Select the View tab.
5. Uncheck the Hide extensions for known file types checkbox.
6. Click the OK button to close the dialog.