Characterization of Magnetic Recording Channels: A Historical Perspective
Speaker:
Thomas D. Howell San Jose State University
Abstract
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 im portant, 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.
Biography
Thomas D. Howell (M'81, SM'89) received the B.S. degree in mathematics from
the California Institute of Technology, Pasadena, CA, in 1973 and the
Ph.D. degree in computer science from Cornell University, Ithaca, N Y, in
1976.
He became a Lecturer in computer science and electrical engineering at San
Jose State University, CA, in 2002. From 1977 to 1990 he was a research staff
member in the IBM Research Division at their San Jose, Zurich, and Almaden
centers, where he conducted research on the application of advanced signal
processing techniques to magnetic recording channels. After joining Quantum
Corporation in 1990, he managed advanced engineering groups in a variety of
areas and helped introduce new technologies including digital channels,
magnetoresistive and giant magnetoresistive heads into the company's
products. He held a number of positions, ending as Vice President of
Research. He served on the board of directors of the National Storage
Industry Consortium and on industrial advisory councils at several university
research centers during the 1990s. Dr. Howell served as an editor of the
IEEE Transactions on Magnetics (1997-2000) and chaired The Magnetic Recording
Conference (2 000). Contact: Dr. Thomas D. Howell, Department of Computer
Science, San Jose State University, One Washington Square, San Jose, CA
95192; telephone: +1 408 924 7171; fax: +1 408 924 5080; e-mail:
t.howell@ieee.org.