PURPOSE: To shorten the time required to start up a system and to improve the performance by employing a new code when firmware is transferred to a RAM.
CONSTITUTION: A nonvolatile memory 16 in incorporated in the device and firmware data arriving from a host computer are written in a RAM area 13 and the nonvolatile memory 16 in the device. When the power source is turned ON, part of firmware data arriving from the host computer is compared with the firmware data saved in the nonvolatile memory 16 and the data are loaded from the nonvolatile memory 16 to the RAM area 13 on condition that they match each other. When they are different, on the other hand, the latest firmware data are transferred to the RAM 13 and executed it to smoothly start up an input/output device including the controller.