INT 15 - SYSTEM - later PS/2s - ENABLE A20 GATE AX = 2401h Return: CF clear if successful AH = 00h CF set on error AH = status 01h keyboard controller is in secure mode 86h function not supported Notes: also supported by AMI PCI BIOS and Qualitas 386MAX v6.01+ IBM classifies this function as optional SeeAlso: AX=2400h,AX=2402h,PORT 0092h