PURPOSE: To process input/output I/O of a large quantity of data in parallel and to shorten the I/O time by divisionally storing the large quantity of data in a memory into plural secondary storage devices.

CONSTITUTION: A system for read/write of large-capacity DB consists of a large-capacity memory 1, plural secondary storage devices 2, a main I/O control part 3 which controls write of the DB from the memory 1 to secondary storage devices 2 and read of the DB from secondary storage devices to the memory 1, and sub-I/O control parts 4 corresponding to secondary storage devices 2. Large-capacity DB is divided to blocks whose number corresponds to the number of secondary storage devices which can be assigned to pertient DB, and one secondary storage device is assigned to each block. Thus, the large quantity of continuous data on the memory is divided to plural blocks and read/write of this data is processed in parallel, and the I/O time is shortened to about 1/m when data is divided to m-number of blocks.