THEORY OF MAGNETIC RECORDING SYSTEMS

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Abstract
Following a review of the theory of recording systems based on particulate media, areas are defined where significant improvements in both theory and practice seem possible. Individual particles switch according to the fanning model. Although a plausible justification is lacking, local field theories appear adequate to describe the M‐H behavior of particulate assemblies. Head fringing fields derived by boundary value techniques are valid providing the permeability remains constant and isotropic. Whilst effects due to the rotating head field and tape demagnetizing fields can be important, in normal operation a much simpler model of the write process suffices. The theory of the demagnetization‐remagnetization cycle occurring between write and read is outlined and recent measurements on high coercivity tape given in corroboration. The read process spectrum is shown to be the Fourier transform of the fringing field which facilitates a unified treatment of analog and digital recording and tape noise. The present level of understanding permits a calculation of the all important tape limited signal‐to‐noise ratios (SNR's), which values are, for audio, instrumentation and video recorders, within 6 db of experiment. This is evidence of the validity of the theory and puts an upper bound upon future improvement of γFe2O3 tape. Artificially constrained (IBM format) and technology limited digital recorders are discussed separately. Finally, areas of probable improvement, such as interaction theory and linearity, the write process, communications theory, tape manufacture, tape materials and ferrite heads are discussed.

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