A special application of information theory to recording systems

Information theory concepts are applied to determine storage capacity and efficiency of recording media and techniques. Because the signal-to-noise ratio is a function of track width, the capacity must be calculated on an area basis. Expressions are derived for the storage capacity as a function of track width and number of levels stored. This provides a means for comparing the efficiency of various recording techniques such as binary digital, multilevel digital and analog. The results are: 1) The maximum information storage capacity of a recording medium can be determined and the degree to which a practical recording system approaches this can be calculated. 2) The information capacity per unit width of tape or per unit area is greatest when the tracks are made as narrow as possible. 3) Binary recording is more efficient than any digital system using a higher numerical base if very narrow tracks can be utilized. 4) When track width is determined by mechanical factors, multilevel digital storage may be most efficient. The optimum number of levels may be calculated from the signal-to-noise ratio of the track. 5) Binary recording is much more efficient than analog recording when high accuracies or large signal-to-noise ratios are desired.