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In this paper, the author describes special techniques to maximize track density in random-access mass storage. In particular, he discusses a servo-access concept that provides self-adjusting head positioning. The paper also discusses in detail a novel method for precisely positioning the recording head and providing track location and registration at 154 tracks per inch.
The IBM 3330 Data Storage Unit, announced in 1970, was the first production disk file to incorporate a track-following feedback control system. In this 1961 Journal paper, Hoagland demonstrated the feasibility of a similar positioning concept, which helped prepare the way for the IBM product. As background, the IBM 3330 was a high-performance, high-capacity direct access storage subsystem for use with all IBM System/370™ models as well as the IBM System/360™ Model 195. Each 3330 subsystem had from two to 16 drives, giving users fast access up to 1.6 billion bytes of online storage. According to E. Pugh, L. Johnson, and J. Palmer, authors of IBM's 360 and Early 370 Systems, the IBM 3330 Data Storage Unit had two notable innovations: the track-following servo system and a voice-coil actuator (similar to the element used to vibrate a loudspeaker diaphragm). This later feature made the unit the first disk storage product to use a voice-coil actuator under control of a track-following servo system. This combination of features provided better response time, higher track density, and more reliable operation than previously attainable.
The author of this paper, Albert Hoagland, is the author of Digital Magnetic Recording, considered by many technologists to be the most important book in the field, and he has received numerous awards for his work in magnetic storage. In 2005, the dean of the Santa Clara University School of Engineering remarked, “Al Hoagland's pioneering work in computer storage, so crucial to the widespread utility of computing in the final four decades of the 20th century, inspired countless hundreds if not thousands of our students.” Hoagland is the recipient of the IEEE Centennial Medal (1984), the IEEE Computer Society Golden Core Award (1996), and the IEEE Third Millennium Medal (2000).
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