INT 21 U - DR-DOS 5.0+ - SHARE/HILOAD CONTROL
        AX = 4457h
        DH = subfunction
            00h enable/disable SHARE
                DL = 00h disable
                   = 01h enable
                   else Return: AX = ???
            01h get HILOAD status
                Return: AX = status
                            0000h off
                            0001h on
            02h set HILOAD status
                DL = new state (00h off, 01h on)
                Return: AX = ???
            other
                Return: AX = ???
Note:   This was seen called by COMMAND.COM of DR-DOS 6.0