Particulate Recording Media

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Abstract
Magnetic recording is a very useful and versatile technology, and one that is continuously evolving to serve the increasing demand for information storage and to meet the challenge of competitors such as optical recording. The basic principles of magnetic recording are described in detail elsewhere and briefly below. The elements of a magnetic recording system are a magnetizable surface layer carried on a flexible tape or on a rotating disk, and a transducer that can both write information to and read information from this surface. The tape or disk, often called a recording medium, and the transducer, called a head, move with respect to each other. The information to be stored is originally contained in an electrical signal, either by direct analog representation or via frequency, phase, amplitude, or pulse-code modulation. In response to this signal, the head in the writing mode generates an intense, localized magnetic field that is capable of changing the direction and degree of the magnetization in the surface material. Each time the input signal changes sign, the writing field changes direction and a transition between regions of opposite magnetization is created. As the head moves along the surface, a series of these transitions is created along a track. The resulting magnetization pattern of the tape or disk becomes itself the source of a spatially varying magnetic field.