A survey of magnetic recording

THE understanding of magnetic recording and playback processes and the applications for magnetic recording have made considerable strides during the last 15 years. In the period of the early 1930´s magnetic recorders had to operate with a recording-medium speed from 5 to 10 feet per second to secure a frequency response from 50 to 5,000 cycles per second. Today it is almost standard practice to achieve the same response characteristic with much higher signal-to-noise ratio and with considerably less distortion even though the medium moves only with a velocity of 2.5 to 3 inches per second. This represents a speed reduction of 20 to 1. The weight reduction is still greater, namely, 50 to 1 since the specific weight of plastic tape is at least 2.5 times less than that of steel tape which was used at that time. No other method of recording, whether mechanical or optical, has made such an advance in such a short period. A brief review of the history of magnetic recording indicates that 20 years ago the available magnetic-recording media with their relatively low coercive force limited the high-frequency response. In about 1936, Vicalloy tape, with more suitable magnetic properties, shifted the burden of improvements to magnetic heads. Then, coated magnetic tape and ring heads made their appearance, both intrinsically capable of a performance characteristic which has as yet not been fully exploited.