Magnetic Spacing Trends: From LMR to PMR and Beyond

This paper examines trends in magnetic spacing in the hard disk drive industry for the last 15 years or so, as we transitioned from inductive to magnetoresistive (MR), giant magnetoresistive (GMR), and tunneling magnetoresistive (TMR) heads, and from longitudinal to perpendicular recording. Historical data show surprisingly good scaling relationships between areal density, linear density, track density, bit aspect ratio (BAR), and magnetic spacing. These trends have held from below 1 Gb/in² until today´s densities, with no significant discontinuities when crossing major technology changes. In particular, it is found that magnetic spacing has scaled with the length of the bit, and more specifically has equaled about half the bit length. Magnetic spacing components, on the other hand, show larger degree of deviations from the trend. Projections to 1 and 10 Tb/in² are made.