INT 2F U - NORTON UTILITIES 5.0+ TSRs - ENABLE
        AX = FE01h
        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
            0002h successful (DISKMON, FILESAVE, EP)
            FE00h successful (NCACHE-x, DISKREET)
Notes:  if the enable/disable calls are used on DISKMON or NCACHE-x, the status
          report generated by the programs still indicates the previous state,
          and DISKMON.INI is not updated
        apparently has no effect on DISKREET
SeeAlso: AX=FE02h