INT 2F U - ??? - GET MEMORY SIZE
        AX = 4A06h
        DX = segment following last byte of conventional memory
Return: DX = segment following last byte of memory available for use by DOS
Note:   called by MSDOS 5.00 IO.SYS startup code if the signature "RPL" is
          present three bytes beyond the INT 2F handler; this call overrides
          the value returned by INT 12