A computer includes a processing unit; a hard disk drive having a main memory region on and from which processing information used in correspondence to processing procedures of the processing unit is directly written and read; a control unit which communicates with the hard disk drive at high speed, for controlling the writing and reading for the hard disk drive; and a communications bus which connects between the hard disk drive and the control unit so that the hard disk drive and the control unit can communicate with each other at high-speed. Accordingly, there is provided a computer which effectively overcomes the limit on a memory storage capacity, and saves the space of a mainboard and reduces the weight thereof.