An improved reading system for magnetically recorded digital data

In magnetic recording of pulses, whether on drum or tape, the resulting flux pattern is affected by proximity of adjacent pulses. The best defined region is that adjacent to the maximum. In reading, the signal is the derivative of the flux. In the best defined region, this is close to a straight line passing through zero when the flux is a maximum. The slope of the curve at the zero changes sign with change of pulse polarity. A new method of reading is described which examines the signal from the head for such transitions from positive to negative or reverse as indications that a positive or negative pulse had been recorded. This is done by gating the inverted signal with the delayed signal for positive pulse reading and the inverse of this for reading negative pulses. Besides providing sharply defined outputs, this method permits reading both positive and negative pulses from a single channel without interference or ambiguity. Examples are given for using this facility for checking purposes and for storage of two types of data in a common channel.