Apparatus for interpreting information recorded on an erasable storage medium, and for making it possible to replace such information in full or in part

Claim 1

In a data-processing system wherein data is selectively recorded in a serial-by-bit mode on an erasable medium and wherein each character is assigned a period of uniform duration although the periods of the ''''1'''' and ''''0'''' bits are not equal to each other the combination comprising: a. a read/write head for reading data from said erasable medium and for writing new data on said erasable medium and simultaneously erasing any data previously recorded on said erasable medium; b. uniquely distinguishable block-indicating signals recorded on said erasable medium as an integral part of the recorded data signal and spaced at equidistant intervals for indicating the initial signal of each block of data; c. drive means for moving said erasable medium at a uniform speed relative to said read/write head; d. a signal source with an adjustable frequency rate for generating signals at approximately the same frequency said uniquely distinguishable block-indicating signals are read by said read/write head when said erasable medium is moved in response to the action of said drive means; e. a comparator having as a first input thereof signals from said signal source and as a second input thereof said uniquely distinguishable block indicating signals as read by said read/write head, for producing an output signal indicative of the magnitude and direction of any frequency difference or phase shift between said first and second input signals; and f. feedback control means coupled to the output of said comparator and to said signal source for adjusting the pulse repetition rate of said signal source to minimize any frequency difference or phase shift between said first and second input signals to said comparator.