INT 12h (18)             Report Memory Size

    Reports the number of contiguous 1K memory blocks in the system (up to
    640K).

       On entry:      No parameters

       Returns:       AX         Memory size (up to 640K)

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       Notes:         This service determines memory by either examining
                      the DIP switches on the system board or using the
                      value stored in the CMOS battery, depending on the
                      type of machine.

                      The value returned in AX is the same as that stored
                      at memory location 0:0413h, which is initialized
                      during the power-up tests.

                      This is the amount of memory available to the entire
                      system. This is not the amount of memory available
                      to the user's program. Use INT 21h, Function 48h, to
                      determine the amount of memory available to a user's
                      program.

                      To determine the amount of memory above the 1024K
                      address range, use INT 15h, Service 88h.

                      If the CMOS battery memory value or the DIP switch
                      value is greater than the actual amount of memory,
                      then the actual amount of memory is returned by this
                      interrupt.