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 thereof, 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 that is 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 at least a 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, wherein the at least one first memory element is a volatile memory element and the at least one second memory element is a non-volatile memory element, wherein the memory includes a controller for controlling memory accesses received from the processor which executes the virtualization management unit, wherein the virtualization management unit is further configured to: monitor usage of the data storage area; select data having an oldest access time or data having a lowest access frequency from the data stored in the working set, in a case where the usage of the data storage area is larger than a predetermined threshold; and output a memory access requesting to write the selected data to the data compression area, and wherein the controller is configured to: read the selected data from the data storage area based on the memory access; compress the selected data; and write the compressed data to the data compression area as compressed data.