INT 15h,  88h (136)      Get extended memory size                  XT-286, AT

    Reports amount of memory above 1024K.

       On entry:      AH         88h

       Returns:       Carry      Set if error, else cleared
                      AX         Number of 1K blocks above 1024K

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       Notes:         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.