Using Assoc and FType to Create a New Type

On page 74 of Windows Command-Line Administration Instant Reference, I describe how to add an Open command to an existing file type, txtfile. The txtfile type already appears in the registry, so adding a new command to it is relatively straightforward. However, what happens if you want to create an entirely new type—one that doesn’t currently exist in the Registry?

Before you can do anything, you need to open an Administrator command prompt because Vista, Windows 7, and anything else newer won’t let you make the required registry changes with a standard account. Follow these steps in order to open an administrator command prompt.


  1. Choose Start > All Programs > Accessories.
  2. Right click the Command Prompt icon and choose Run As Administrator from the context menu. You’ll see a User Account Control dialog box.
  3. Click Yes. You’ll see a new command prompt open. However, instead of the usual title bar entry, you’ll see Administrator: Command Prompt. In addition, instead of opening to your personal user folder, the prompt will display C:\Windows\system32>. If you don’t see these differences, then you haven’t opened an administrator command prompt.

Let’s say you want to include a new file extension and it’s associated type. For example, you might want to create a .RIN file extension and associate it with a type of RINFile. Once you create this association, you may want to use Notepad to open the file. In order to perform this task, you need to use two different utilities as shown in the following steps.


  1. Type Assoc .RIN=RINFile and press Enter. You’ll see, “.RIN=RINFile” appear at the command line. This command creates a .RIN file extension entry in the Registry as shown here.
  2. Type FType RINFile=%SystemRoot%\Notepad.exe %1 and press Enter. Notice that you don’t enclose the command in double quotesit will fail if you do. You’ll see, “RINFile=C:\Windows\Notepad.exe %1” (or something similar) appear at the command line. This command creates the RINFile association in the Registry as shown here.
  3. Create a new .RIN file on your hard drive. You don’t have to do anything with it, just create the file.
  4. Double click the new .RIN file. Windows will open the file using Notepad.

This technique works with any file extension and association you want to create. In fact, you could easily create a batch file to patch user configurations where the file associations have become damaged in some way. The big thing to remember is that this is always a two-step process when the file extension doesn’t already exist or the association is new. Use the Assoc utility to create a link between any file extension and it’s association and the FType utility to create the association itself. Let me know if you have any questions about this technique at


Author: John

John Mueller is a freelance author and technical editor. He has writing in his blood, having produced 99 books and over 600 articles to date. The topics range from networking to artificial intelligence and from database management to heads-down programming. Some of his current books include a Web security book, discussions of how to manage big data using data science, a Windows command -line reference, and a book that shows how to build your own custom PC. His technical editing skills have helped over more than 67 authors refine the content of their manuscripts. John has provided technical editing services to both Data Based Advisor and Coast Compute magazines. He has also contributed articles to magazines such as Software Quality Connection, DevSource, InformIT, SQL Server Professional, Visual C++ Developer, Hard Core Visual Basic, asp.netPRO, Software Test and Performance, and Visual Basic Developer. Be sure to read John’s blog at When John isn’t working at the computer, you can find him outside in the garden, cutting wood, or generally enjoying nature. John also likes making wine and knitting. When not occupied with anything else, he makes glycerin soap and candles, which comes in handy for gift baskets. You can reach John on the Internet at John is also setting up a website at Feel free to take a look and make suggestions on how he can improve it.