152400 INT 15 - SYSTEM - later PS/2s - DISABLE A20 GATE
152401 INT 15 - SYSTEM - later PS/2s - ENABLE A20 GATE
152402 INT 15 - SYSTEM - later PS/2s - GET A20 GATE STATUS
152403 INT 15 - SYSTEM - later PS/2s - QUERY A20 GATE SUPPORT