Write processes in high density recording

The ac biased and unbiased write processes in digital recording are compared using the Preisach diagram. Whereas differences occur at low densities, the high density Preisach representations become indistinguishable, provided that the same total write field is used for sharp digital transitions in a "run-length-limited" (Manchester, Miller) code. Since the output waveforms are then identical it follows that the same input-output relationships occur even when ac bias is not used.