A beam steering system having first diffraction gratings, each one being associated with a corresponding one of a first plurality of grating vectors disposed substantially in a first plane. In some embodiments, the tailgate cover includes two or three pockets. Partial array self-refresh configuration settings are independently made. The second external connection terminal is connected to the second semiconductor element, and the second external connection terminal is configured to be, together with the first external connection terminal, connected to a wiring board. Access frequency is monitored and data is copied based on the monitored access frequency.