US Patent 7523229 Memory protection during direct memory access

An I/O controller to which an I/O device is connected includes a DMA controller (DMAC) and an access control unit (ACU). The DMAC executes DMA transfer in accordance with data transfer control information set in a control/status register by a user process. The ACU limits execution of DMA transfer by the DMAC based on access control information set in a control/status register by a privileged process, and disables the DMAC from accessing any memory area other than the memory area that can be accessed by the user process.