A hard disk assembly includes a first and a second hard disk, and a hard disk connecting mechanism for holding the first and the second hard disks. The first and second hard disks both each have a composite receptacle. The hard disk connecting mechanism includes a frame for mounting the first and the second hard disks and a composite connector detachably positioned in the frame. The composite connector includes a base, a first composite plug engaged with the composite receptacle of the first hard disk and a second composite plug engaged with the composite receptacle of the second hard disk.