PURPOSE:To reduce overhead accompanied by means of queueing control to the utmost by enqueuing to a different queue in correspondence with an enqueue cause at the time of enqueuing input/output start and independently dequeuing the queue when a dequeue cause which corresponds at every queue occurs. CONSTITUTION:When one sub-channel 20 is enqueued by plural queues at certain time, starting begins in accordance with the queue which is dequeued very faster. When the queues are dequeued, data is recorded in the sub-channel 20. Thus, excess starting is prevented. When plural sub-channels 20 are enqueued by one queue in a system, overhead by the idle queues becomes small. A part executing a queueing processing can be realized by sharing the hardware of a central processing unit.
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