Int 21/AX=4101h/DX=FFFEh

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

Category: Security - Int 21h - S