Understanding File Types and Extensions

by Barry Dysert
(last updated December 4, 2017)

Whenever you are working in Windows, you are ultimately working with one or more files of various types. All files have names, and each name is broken into pieces. For example, given a file name of "C:\Temp\MyFile.txt", the first piece ("C:") is the disk name. The next piece ("\Temp") is the folder or directory name, and the "MyFile.txt" piece is the actual file name. The file name itself is further broken into two pieces, with the "MyFile" being the base file name and the ".txt" being the file type or extension.

A file's type is very important. It tells Windows what kind of file it is and therefore what program should be used to open the file. For example, a file type of ".txt" tells Windows that this is a text file and should be opened (by default) with Notepad. A file type of ".xlsx" tells Windows that this is an Excel workbook and should be opened (by default) with Excel.

There are thousands of different file types and corresponding programs used to open them. You can even add more file types of your own and associate them with whatever programs should be used to open them. Moreover, you can always change which program is used to open which file type.

Before working with file types, you should configure your system so that file types are displayed. There is an option in Windows to hide known file types, but turning that option off allows you to see the types. You turn on the displaying of file types by following these steps if you are using Windows 8 or Windows 10:

  1. Display the Control Panel.
  2. Click the Appearance and Personalization link. (See Figure 1.)
  3. Figure 1. The Appearance and Personalization area of the Control Panel.

  4. Click the Show Hidden Files and Folders link. Windows displays the Folder Options dialog box.
  5. Make sure the View tab is displayed. (See Figure 2.)
  6. Figure 2. The View tab of the Folder Options dialog box.

If you are using Windows 7, follow these steps instead:

  1. Go to the Control Panel (click the Start menu and then click Control Panel).
  2. Click the Tools link.
  3. Click the Folder Options link. Windows displays the Folder Options dialog box.
  4. Make sure the View tab is displayed.

Regardless of the version of Windows you are using, by deselecting the Hide Extensions for Known File Types check box, you will be able to see the types of all your files in Windows Explorer or File Explorer. Once you've set up your system to display the file types, it's much easier to work with them.

 This tip (12065) applies to Windows 7, 8, and 10.

Author Bio

Barry Dysert

Barry has been a computer professional for over 30 years, working in different positions such as technical team leader, project manager, and software developer.  He is currently a senior software engineer with an emphasis on developing custom applications under Microsoft Windows. ...

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