Characterization of Magnetic Recording Channels: A Historical Perspective

The design of advanced signal processing systems for recovering data stored on magnetic media requires an accurate understanding of the input/output characteristics of the storage system. The designer must be able to predict the output resulting from an arbitrary input in order to select the optimum set of signals to represent the data. He or she should also know the statistical properties of the noise and the types of distortion affecting the storage and readback processes.

Early systems used simple models of channel behavior. As densities increased and signal processing schemes became more complex, more sophisticated models were needed. It is interesting to observe how effects once considered negligible became important, and conversely, how dominant distortions, once understood, became part of the expected signal and hence of negligible importance as disturbances.

In this lecture I will examine selected developments from the history of magnetic recording channel characterization. I will discuss the changing roles of intersymbol interference and nonlinear transition shift, along with some of the techniques used to measure and model them. Magnetic recording systems continue to evolve at a rapid pace; the lessons learned from history often help speed progress and avoid future pitfalls.