Computer system with an input/output processor which enables direct file transfers between a storage medium and a network

A data processor transfers files at high speeds from a magnetic disk or other storage media to a network and shortens the processing time for the file transfers. An I/O processor includes (i) a channel to which a magnetic disk is connected, (ii) a LAN adapter to which a network is connected, (iii) a switch for switching and connecting the channel and LAN adapter, and (iv) a channel controller for controlling the channel, the LAN adapter, and the switch. The channel controller controls the channel, the LAN adapter, and the switch in accordance with a data transfer start instruction from an instruction processor. The channel reads data from the magnetic disk and transfers it to the LAN adapter via the switch. The LAN adapter sends the data to the network or reads data from the network and transfers it to the channel via the switch. The channel sends the data to the magnetic disk.