Part of Hard Disk

The hard disk platters are accessed for read and write operations using theread/write heads mounted on the top and bottom surfaces of each platter. Obviously, the read/write heads don't just float in space; they must be held in an exact position relative to the surfaces they are reading, and furthermore, they must be moved from track to track to allow access to the entire surface of the disk. The heads are mounted onto a structure that facilitates this process. Often called the head assembly or actuator assembly (or even the head-actuator assembly), it is comprised of several different parts.
The heads themselves are mounted on head sliders. The sliders are suspended over the surface of the disk at the ends of the head arms. The head arms are all mechanically fused into a single structure that is moved around the surface of the disk by the actuator. (Sort of like "the leg bone's connected to the knee bone", isn't it? :^) ) It would be an understatement to say that these components are neglected; heck, most people don't even know they exist! Yet they play an important role in the function and performance of the drive. In particular, advances in slider, arm and actuator design are critical to improving the seek time of a hard disk; the impact that the actuator has on performance is discussed in this section.