Windowed VDMs in x86-Based Machines
Each MS-DOS application runs as a Windows VDM, which in turn, runs as a console manager application in the Win32 protected subsystem.
In NT-based operating system platforms, a kernel-mode component called the V86 emulator traps I/O instructions issued by MS-DOS applications. As long as such an application runs within a window, its attempts to access video adapter ports are trapped and reflected back to the system-supplied video VDD, which emulates the behavior of the adapter for the application.
In other words, the display driver retains control of the video adapter while a VDM runs in a window.