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Category: vendor-specific BIOS extensions

INT 15 - SYSTEM - later PS/2s - DISABLE A20 GATE

	AX = 2400h
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
BUG:	AMI BIOS v1.00.03.AV0M never reports an error on failure to disable
	  the A20 gate; it simply writes 0 to PORT 0092h
SeeAlso: AX=2401h,AX=2402h,AX=2403h,PORT 0092h

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