Int 15h, 88h            Get extended memory size                   XT-286, AT

    Reports amount of memory above 1024K.

        Entry   AH = 88h

        Return  CF   Set if error, else cleared
                AX = Number of 1K blocks above 1024K

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    This service is available only for the AT and XT-286.

    The amount of memory returned by this service is stored in the
    CMOS battery. It is determined and set during power-on.

    For the memory above the 1024K range to be usable, the planar
    memory (memory on the system board) must be fully populated. The
    memory above the 1024K range is often called "extended" memory.