INT 2F - AD-DOS - INSTALLATION CHECK AX = 0C00h Return: AL = FF if installed BX = 4144H ('AD') CX = 2D44H ('-D') DX = 4F53H ('OS') Notes: AD-DOS is the DOS version of the After Dark screen blanker for MS Windows AH=0Ch is the default multiplex number (there is one report of a version with AH=C0h as default)