Abstract: A hard disk driving device in which a plurality of hard disks each formed with a magnetic recording layer are secured to the same rotational shaft in a predetermined spaced relation, and a magnetic head mounted on a floating (flying) type head slider is disposed on each surface, characterized in that an area of a portion concerned with flotation of a head slider provided on a head slider assembly sandwiched between adjacent hard disks is made to be smaller than an area of a portion concerned with flotation of a head slider provided on a head slider assembly sandwiched between adjacent hard disks.

Abstract: A tracking device has a linear motor having a driving coil, a speed sensor having a detection coil, and a moving member reciprocated in a predetermined range together with the driving coil and the detection coil. The moving member receives a driving force upon application of a current to the driving coil, and the detection coil generates a signal according to the speed of the moving member. The speed sensor includes two coils connected with each other in such a direction as to phase-cancel an induced voltage due to a magnetic field generated by the driving coil; at least one of the two coils is the detection coil. The detection coil and the driving coil are arranged on one side of the moving member in a single unit.