When you exit an MS-DOS-based application, Windows XP returns to the command interpreter, Cmd.exe. When you run a terminate-and-stay-resident program (TSR) or temporarily suspend an MS-DOS-based application to return to the command prompt, Windows XP runs the command interpreter for the MS-DOS environment, Command.com. This preserves the MS-DOS environment, allowing you to use the TSR immediately.
Because starting and running other types of applications from the Command.com prompt can disrupt a TSR or suspended MS-DOS-based application, Windows XP provides dosonly. With dosonly, you can start only MS-DOS-based applications from the Command.com prompt. You can include dosonly in your Config.nt file or the equivalent custom startup file in an application's program information file (PIF).