INT 2F U - NORTON UTILITIES 5.0+ DISKMON, FILESAVE / EP - internal - ???
        AX = FE04h
        DI = 4E55h ("NU")
        SI = TSR identifier (see AX=FE00h)
Return: SI = TSR reply (lowercase version of entry SI, i.e. SI or 2020h)
        AX = status
            0008h successful???