PURPOSE: To quicken dumping process and improve operation efficiency of a central processing unit by adding the second virtual memory area to the central processing unit system and dumping information of real memory area when occurrence of impediment, and operating the system using the second virtual memory area in place of the virtual memory.

CONSTITUTION: The second direct access memory DASD5 is added, and when an impediment occurs at point A during operation of the CPU1 and operation of the system becomes impossible, information stored in a main memory MSU2 is shunted to a magnetic tape device MT4 and stored in MT4. This transfer is made immediately without needing time. The CPU1 cuts off DASD3 and combined with the second DASD5, and program restoring IPL is executed and operation of the CPU1 is started. When necessary afterward, data at the time of occurrence of impediment is dumped from DASD3 and MT4.