Abstract: A magnetic disk apparatus includes at least two systems, each system having at least one power unit and at least one battery unit ancillary to the power unit. The disk apparatus also includes at least one common power unit having a pluralities of batteries attached thereto connected in common with the two systems. Patrol control means (PC) is operatively connected to a power control unit (0) of one system and a power control unit (1) of another system for giving a control signal during a battery monitoring operation and a priority order to the battery monitoring operation. The patrol control means monitors the function of the common batteries attached to the common power unit and, further, when the common batteries are incorporated in the magnetic disk apparatus, controls the simultaneous monitoring of the common batteries and the time of incorporation of the common batteries into the magnetic disk apparatus.

Abstract: A magnetic disk apparatus which is used as a subsystem of a computer system, in particular a medium-sized computer system which uses commercial power and does not have its own backup power, provided with a plurality of directors (118), a plurality of magnetic disk modules (148) commonly accessed from the plurality of directors, a plurality of director batteries (114-m) for supplying power individually to the plurality of directors, magnetic disk module batteries (114-n) for supplying power to the magnetic disk modules, and a power controller (110) for independently controlling the supply of power from the plurality of director batteries and magnetic disk module batteries in accordance with the operating state of the plurality of directors and magnetic disk modules. (FIG. 1).