FILE I/O CONTROL DEVICE WRITING BLOCKS TO FASTER DEVICE FIRST AND CANCELING EXCLUSIVE LOCK AS EACH BLOCK IS WRITTEN

A file input/output control device for a computer system of the present invention can, even in an environment where magnetic storage and semiconductor storage devices with quite different access speeds are concurrently used as the external storage, cancel exclusive control for film blocks without deteriorating the performance of higher speed storage. For this purpose, this device is provided with block write means to write the blocks in the buffer to the external storage block by block when a quiet point of the processing program is established and exclusion cancellation means to, each time the block write means terminates writing for a block, cancel exclusive control for that block.