Windows Vista has GUI (graphical user interface) for editing, changing or setting file associations from various file types and protocols to open with a default program. However, it doesn’t provide a tool or utility to unassociate file types and remove file extension associations that already exists in the registry.

Windows Vista does have two command link utilities that can be use to remove all file extension associations with its default program. Here’s the guide on how to use the assoc and ftype commands to remove file type association of an extension.

Example removing .rar extension associated “to open “with winrar.exe

1. Open an elevated command prompt with admistrator privileges.

2. Remove the file extension association from its assigned file type with the following command, follow by ENTER:
assoc .ext=

Replace .ext with the extension name that needs to be unassociated. For example, to disassociate WinRAR .rar extension, simply type assoc .rar =.

Note that after disassociation of file extension from file type, the default program for the file type no longer been shown in the “Open With” list for the file extension.

3. Then, clear and delete the default program used for the open command when launching files of this type by typing the following command, and press ENTER:

ftype FileType=

Replace FileType with the actual name for the file type associated to the file extension to be removed from the system. For example, for WinRAR, type ftype WinRAR=.

Note that if you don’t know what’s the correct “FileType” to type, simply type assoc (associated file type will be shown after the extension) or ftype to get a listing of all file types defined in the system.

After disassociation or unassociation of a file extension association, when user double clicks on the particular type of file, the dialog box will be prompted saying “This file does not have a program associated with it for performing this action. Create an association in Set Associations control panel.” and user is forced to click the only OK button. However, it’s possible to right click on the file, and choose Open With… option, then user can select a program from a list of install programs to open the file, and on the same time, set the correct and proper file association again.