An I/O controller and method are provided. The I/O controller to which an I/O device can be connected, and instructs the I/O device to execute a process includes a descriptor transfer device that transfers a descriptor indicating contents of a process to be executed, and execution instruction unit that instructs the I/O device to execute the process, based on the descriptor transferred from the descriptor transfer device, wherein the descriptor transfer device includes a memory for storing the descriptor; descriptor reading unit that reads, according to an indication regarding a descriptor read source from a processor, an indicated descriptor from a main memory or said memory which stores the descriptor, and descriptor transfer unit that transfers the read descriptor to the execution instruction unit.