Power consumption decrease memory management method

The power consumed by a memory is reduced without affecting the performance whereby a processor accesses the memory. A state of a power supplied to the memory is controlled to one of an active state wherein a storage area included in the memory rank can be accessed from the processor, and an inactive state wherein access cannot be performed without a delay for each memory rank, the basic system software prevents fragmentation in which the allocated storage area spans a plurality of memory ranks, puts the power state of a memory rank which does not include an allocated storage area into the inactive state, and puts the power state of a memory rank which includes a storage area required for allocation first into the active state.