Windows NT, through a component of Win32, supports the concept of Virtual DOS Machines (VDMs). VDMs create the virtual hardware and software environment expected by DOS-mode programs. Every DOS program executes as a single thread and it thinks that it has an entire computer to do so.

  • Software
    In Windows NT, NTVDM.EXE translates DOS calls into Win32 calls and forwards it to the Win32 subsystem. NTIO.SYS and NTDOS.SYS are the equivalent of the IO.SYS and MSDOS.SYS files. VDMREDIR.DLL redirects the file subsystem and input/output requests to the Win32 subsystem.

  • Hardware
    The virtual hardware is created using Virtual Device Drivers (VDDs). The VDDs intercept requests to hardware devices, such as the mouse, keyboard, serial ports, etc., and redirects them to the Win32 subsystem.

    The VDDs are read from the CONFIG.NT and AUTOEXEC.NT files, and correspond to their CONFIG.SYS and AUTOEXEC.BAT files respectively.