An electronic device includes a base, two parallel mounting plates extending from the base, and a dummy hard disk drive. Each of the mounting plates defines two mounting holes. The dummy hard disk drive includes a bottom plate, two side plates pivotably mounted to two opposite sides of the bottom plate, and two end plates pivotably mounted to two opposite ends of the bottom plate. Two mounting rods extend from an outer surface of each of the side plates. The side plates and the end plates can hinge so as to be substantially perpendicular to the bottom plate, to form a hollow rectangular frame. The mounting rods are inserted in the corresponding mounting holes, to mount the dummy hard disk drive between the mounting plates.