A disk file comprises a disk stack subassembly and a head positioning actuator each mounted on opposite sides of a central box frame. The disk stack subassembly has a non-rotating central spindle and an in-hub electric motor whose stator is mounted on the spindle. The rotor of the motor is mounted internally of a hub supported for rotation about the spindle by two bearings at opposite ends of the spindle. A stack of disks is mounted externally on the hub. The box frame is open to one side and the opposite ends of the stationary spindle are located and fixed in the frame so that the disk stack subassembly spans the open side. Because of the symmetry and rigidity of the design, susceptibility to thermal or vibration induced misregistration is reduced. Finally a cover completes the enclosure.