Abstract: A head disk assembly ("HDA") comprises an enclosure including a base and a pivot bearing cartridge having a shaft and a outer shell rotatable about the shaft. The outer shell has a cylindrical surface. The shaft is affixed to the base at a predetermined location. The enclosure has an internal volume with a limited height above the predetermined location. The cartridge has an elongated portion in the volume, the elongated portion having a height approximately equal to the limited height. The HDA further comprises a plurality of rotating disks, each having at least one recording surface. The HDA further comprises an arm stack comprising a plurality of arms, and a plurality of head gimbal assemblies. Each arm has a stacking portion and a cantilever portion. Each head gimbal assembly has one end attached to the cantilever portion of a respective arm and has an opposite end positioned adjacent a recording surface.