PURPOSE: To attain correspondence without increasing hardware even if the number of the request sources of an input output interruption increases by providing a request representative display means registering request existence information instructing the existence of input output interruption requests in a system controller.

CONSTITUTION: When IOP 5 detects the input output interruption request from one of channels CH5a-CH5n, it stores request source information of the input output interruption request concerned in ISIDA4a in HSA4. When IOP 5 terminates the storage of request source information, it gives the interruption request to SC2. At that time, a control code 36 as shown in figure is issued from IOP 5 to SC 2, for example. The code 36 shows that it is the input output interruption request by the value '10' of a bit 0 and a bit 1, and the 'A0A1' of a bit 6 and a bit 7 shows the logical partition number of the encoded interruption request destination. When SC 2 receives the code 36, it sets the input output interruption requests FF2a-2d provided in correspondence with respective logical partitions.