Expansion unit setup control method that allocates predetermined I/O resources not currently used in processing and later deallocates said I/O resources upon completion of setup

1. Field of the Invention An expansion unit control method for use with an expansion control unit containing at least one device, includes allocating a predetermined input/output (I/O) resource, ensured not to be used in processing, to the at least one device as an I/O resource used for sending and receiving information, performing a predetermined process for the at least one device by sending and receiving information to and from the at least one device through the predetermined I/O resource, and deallocating the predetermined I/O resource allocated to the at least one device.