A hard disk drive controller including a determining unit that determines an external dimension of a hard disk drive that is provided with a motor for rotating a hard disk and a head that is retractable from the hard disk; and a changing unit that changes control of the hard disk drive device according to the external dimension that has been determined by the determining unit. An image forming apparatus is also disclosed which includes the determining unit, the changing unit, and an energy saving shifting unit that shifts the image forming apparatus into an energy saving mode in certain conditions which have been determined in advance. A storage medium on which a program for execution on a computer is stored, the program having the function of the determining unit and the function of the changing unit, is also disclosed.