DETERMINING IF AN XMS DRIVER IS INSTALLED

The recommended way of determining if an XMS driver is installed is to
set AH=43h and AL=00h and then execute INT 2Fh.  If an XMS driver is
available, 80h will be returned in AL.

        Example:

        ; Is an XMS driver installed?

        mov     ax,4300h
        int     2Fh
        cmp     al,80h
        jne     NoXMSDriver