User:Johnburger/Demo/BIOS/A20

The A20 gate has a defined BIOS handler for it - but surprisingly it is not always implemented by BIOS manufacturers. This page in the Wiki describes the recommended sequence of steps to perform - this is Step 2.

Demo/BIOS/A20.inc

;
; BIOS/A20.inc
;

; These are the definitions for the BIOS A20 controller
BIOS.A20.Int    EQU             15h
BIOS.A20.Fn     EQU             24h
BIOS.A20.Enable EQU             01h
BIOS.A20.Disable EQU            00h