Conventionally, there are two kinds of storage devices, i.e., a high-speed volatile storage device and a lower-speed nonvolatile storage device than the volatile storage device. By a conventional technique, it is not possible to directly refer to data in the nonvolatile storage device from a processor of a computer. The data stored in the nonvolatile storage device is loaded into the volatile storage device before used.
Such a conventional technique does not consider access efficiency to the storage device.