Int 2F Fn 4308  U - Himem.sys V2.77+ - Get A20 Handler Number              [m]

   AX = 4308h

Return: AL = 43h if supported
       BL = A20 handler number (value of /MACHINE:nn switch)
       BH = AT A20 switch time (00h medium, 01h fast, 02h slow)

See Also: AX=4309h,AX=4330h