GB1285729A - Reading and writing information on a storage medium - Google Patents

Abstract

1285729 Data storage SINGER NV 23 Dec 1969 [27 Dec 1968] 62631/69 Heading G4C The frequency of clock pulses for interpreting digital data on a movable, erasable, storage medium is synchronized with the speed of the storage medium during read or write operations by reading markers in the data track. Non- return to zero information pulses are stored on a disc, a binary 0 having a pulse width twice that of a binary 1. Each character has the same length however by adding blank spaces to the 0's and 1's, and the first pulse of each character is read as a clock pulse. The read head 1 selects the first pulses and feeds them to a logic circuit 2 where they are lengthened (Fig. 4, waveform B, not shown). A clock pulse generator 3 feeds its pulses through a frequency divider 4 to a comparator 5 having the pulses of waveform B as its other input. Any difference between the frequency of the first pulses from head 1 and the clock generator 3 frequency causes negative feedback which causes a corresponding adjustment of the frequency of generator 3. This is said to be of use when writing fresh data on parts of an already written disc. A counter may be used to distinguish binary 0 and 1.