What method can I use to open an unregistered program?

Q: When opening a file that is not recognized by Windows 98, you will be asked to choose which program to open. If you don't know what program to open this program, you will generally choose to use Notepad, how to change other programs next time? And “ always use this program to open this type of file & rdquo; options, sometimes tick Sometimes, but not. Why is this?
A: When the Open Mode menu appears, it means that the file type is not registered in Windows. For those file types that are not registered, Windows 98 does not know which program to use to open, so a menu will appear. If the file type is first opened and no open program is specified, there will be an option to always open this type of file with this program when the menu is opened for the specified program to open. This option is checked as soon as the specified program is opened for the first time, and the next time you open this type of file, it will run with the program you used to open the first time. For example, if you want to open the Pdos.def file, because the file type of .def is not registered, a program menu will appear when you open the file. You need to specify the program to open the file. If you choose Notepad (Notepad) ), and check "Always open this type of file with this program" option, when you open the extension DEF file later, it will open in Notepad. If you want to open the DEF file with another program, you can hold down the “Shift” key and right click on the file, select "Open" from the right-click menu, and select the open program.