INPUT/OUTPUT CONTROL SYSTEM FOR EXTENDED STORAGE DEVICE

PURPOSE:To efficiently perform input/output control over the extended storage device by, performing load control over a data transfer request to the extended storage device by an arithmetic processor and an input/output processor and performing well-balanced allocation. CONSTITUTION:When a transfer system selecting means 38 selects asynchronous transfer, an asynchronous transfer request quantity adding means 29 counts up the number of requests to areas corresponding to input/output processors 15-18 which perform the transfer of an asynchronous transfer state table 26. The requests are counted down by an asynchronous transfer request quantity subtracting means 28. A 1st asynchronous transfer selecting means 32 refers to the asynchronous transfer state table 26 when the asynchronous transfer is selected and totalizes the number of asynchronous transfer requests to the input/output processors 15-18 connected to system controllers 19 and 20. An input/output processors which is small in the number of requests among input/ output processors connected to the system controller which is less in the number of requests is selected as an input/output processor for synchronous transfer.