In Windows NT, each MS-DOS-based application and 16-bit Windows-based applications run in a Windows NT virtual MS-DOS machine (NTVDM), a single-threaded process that supports 16-bit applications in a 32-bit environment. Windows NT includes the necessary virtual device drivers (VDDs) for the mouse, keyboard, printer, COM ports, and network support. The VDDs are loaded into every VDM based on values stored in the Registry. Information about VDDs is found in the following Registry path:
HKEY_LOCAL_MACHINE\System
\CurrentControlSet
\Control
\VirtualDeviceDrivers
The system manages any changes to the VDD entries automatically when you add a device driver by using Windows NT Setup.