Fundamental Concepts and Units in Magnetism and Magnetic Recording

Abstract

Our generation has seen a dramatic change in the way in which information is stored and retrieved. For almost 500 years, since the invention of movable type, the principal method of storing information was through the printed word. About 100 years ago, methods for analog recording were developed, but these methods have seldom been used for information storage and have mainly been applied to the storage and retrieval of music. About 50 years ago, magnetic recording was developed for analog signals and in the last 25 years magnetic recording has become an important method for storing information in digital form. As more information was created with time, it became essential to improve the efficiency of information storage. Hence the technology for information storage has improved from ca. three letters or characters per cm2 in Gutenberg books, to ca. 20 letters or characters per cm2 in this book, and to ca. 170 letters or characters per cm2 in the microprint edition of the Oxford English Dictionary.[1] Such books have the disadvantage of relatively low storage density but the advantage of rapid access by the final user, the reader, at least if his library contains the appropriate books. This storage density can be improved somewhat through the use of microfilm and micro-photographic techniques, but with the added disadvantage of more difficult access by the reader. Figure 1 shows the improvement of areal storage density with time.