Int 2F Fn 0800  U - Driver.sys Support - Installation Check                [D]

   AX = 0800h

Return: AL = status
       00h not installed, OK to install
       01h not installed, not OK to install
       FFh installed
Desc:  determine whether the internal support code used by DRIVER.SYS is
     present; it is always present in DOS 3.2+

Note:  supported by DR DOS 5.0 and Novell DOS 7