Modeling Computer Hard-Drive Read/Write Heads:  Considerations from Mechanics and Fluid Dynamics



In most hard disk drive designs, the read/write head is very close to the spinning data disk surface, but it does not touch.  It is important to be very close to the disk because this limits how much data can be fit onto the disk.  It is also important not to touch (or "crash") into the disk surface because that can cause data loss and permanent damage to the disk, the read head, or both.  In practice, hard drives establish what is "close but not too close" by balancing mechanical forces imposed on the read head by the positioning arm with a lift force.  The lift is a fluid dynamics effect generated by the flow of air being dragged along by the spinning disk and passing under the read head (also called a "slider bearing").




Figure 1.  Hard disk surface, positioning arm, and read/write head.



  Improving disk storage capacity, reliability, and access speeds require more careful study of the design of the read/write head.  In this problem, we will consider the influences of different geometric and mechanical factors on the performance of slider bearings.  The fluid dynamics describing the lift force on the slider can be derived from the Navier-Stokes equations using the classical lubrication approximation.  Questions of interest will include how the shape and mechanical properties of the slider change the lift and stability in the system.  We will consider how changes in the parameters describing the air flow and the slider design effect the model.  We will try to determine what properties lead to an "optimal slider design."



Figure 2.  Close up of a read/write head.




References on lubrication theory and slider bearings:




Recent article on slider bearings in hard disk drives: