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The traditional, and so far highly successful, approach to continuously improve disk drive performance is based on a scaling principle. In order to gain a twofold increase in areal density, the relevant head and medium dimensions such as head gap, trackwidth, medium grain size, medium thickness, and magnetic spacing are reduced by the square root of two. The resulting loss of the signal amplitude is compensated by more sensitive read head design. Less traditional approaches such as proximity recording, contact recording and keepered recording, have also been proposed, and practiced with various degrees of success. While the areal densities in disk drives are limited by practical engineering considerations, there are several ultimate limits to conventional longitudinal magnetic recording on continuous magnetic medium. This chapter discusses these limitations. One such limitation is related to the magnetic grain size and the thermal stability of written bits. Another limitation is the achievable recording materials of the head and medium and by the write electronics. |
