Data transfer system

Abstract

In a highspeed and large-capacity data transfer operation effected between an extended storage unit and an input/output unit, such a data transfer system is provided, capable of preventing a performance deterioration caused by a lack of main storage capacity with employing a buffer having a large memory capacity, and deterioration of a transfer throughput caused by an overhead of an input/output operation due to a use of a buffer having a small memory capacity. There are provided a CCW for directly designating the extended storage unit as an object of a data transfer operation, and a signal line for initiating from a channel the data transfer operation between HSA-extended storage unit. Furthermore, buffers having the planes and with a small memory capacity are prepared on the HSA. The data transfer operation is carried out between the channel and the buffer with one plane, and the data transfer operation is performed between the extended storage unit and the buffer having the other plane in parallel with the first-mentioned data transfer operation. After the data transfer operations have been accomplished, a data transfer operation for the next block is executed by substituting one plane with the other plane.