Compatibility: EMS 3.2+
Expects: AX    4300H
BX    number of pages requested (16K units)
Returns: AH    EMM status (0=successful)
DX    EMM handle of allocated memory (if successful)
Info: Allocates EMS memory.

The handle returned in DX is used in subsequent calls to map the
EMS into the page frame and other operations.

Notes: Use INT 67H 4200H to see how much EMS is available.

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INT 67H 4300H: Open EMM Handle and Allocate Memory