THE PROGRAMMING API

The XMS API Functions are accessed via the XMS driver's Control
Function. The address of the Control Function is determined via INT 2Fh.
First, a program should determine if an XMS driver is installed.  Next,
it should retrieve the address of the driver's Control Function.  It can
then use any of the available XMS functions.  The functions are divided
into several groups:

        1. Driver Information Functions (0h)
        2. HMA Management Functions (1h-2h)
        3. A20 Management Functions (3h-7h)
        4. Extended Memory Management Functions (8h-Fh)
        5. Upper Memory Management Functions (10h-11h)