Int 15 Fn 2403  - System - Later Ps/2s - Query A20 Gate Support            [b]

   AX = 2403h

Return: CF clear if successful
       AH = 00h
       BX = status of A20 gate support
       bit 0: supported with bit 1 of I/O port 92h
       bit 1: supported on keyboard controller
       bit 15: additional data is available (location not yet defined)
   CF set on error
       AH = status
       01h keyboard controller is in secure mode
       86h function not supported

Note:  also supported by Qualitas 386MAX v6.01+

See Also: AX=2402h