INT 16 U - PC Tools v5.1-8.0 DESKTOP - CHECK WHETHER DESKTOP LOADED RESIDENT
        AX = FFC5h
Return: BL = nonzero if loaded resident
           = 00h if nonresident
Note:   available only when popped up; should call AX=FFEFh first to ensure
          that DESKTOP is active
SeeAlso: AX=FFEFh,AX=FFF3h

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