1. A computer comprising: a processor; a memory coupled to the processor; and an I/O device coupled to the processor, the memory including at least one first memory element and at least one second memory element different from the at least one first memory element in characteristics, wherein a memory area provided by the at least one second memory element includes a data storage area and a data compression area, wherein the computer further comprises a virtualization management unit for managing at least one virtual machine allocated computer resources of the computer, and wherein the virtualization management unit is configured to: set a working set for storing data required for processing performed by a virtual machine in generating the virtual machine, and control data stored in the working set in such a manner that part of the data stored in the working set is stored in the data compression area based on a state of accesses to the data stored in the working set.