Int 21 Fn 4101  - Softlogic Data Guardian - ???                            [y]

   AX = 4101h
   DX = FFFEh

Return: AX = 0000h if installed

Note:  resident code sets several internal variables on this call

See Also: AH=3Fh"NB.SYS",INT 16/AX=FFA3h/BX=0000h