Abstract: A digital correlator compares two digital words a plurality of times. Each time the second digital word is shifted by one additional bit with respect to the first digital word. The results of the various comparisons are stored. The stored results are then searched to find the location of the results indicating the greatest similarity between the bits of the first and second digital words. This location is indicative of the number of bits by which the second digital word is displaced with respect to the first digital word when greatest similarity occurs.

Abstract: A memory protection arrangement includes a primary power supply unit and a back-up battery. The back-up battery supplies maintenance energy to the memory itself, the battery being automatically effective whenever the primary power supply voltage decays to a value less than that of the battery. There is also provided apparatus which is responsive to a failure of the main power source to effect the application of a control signal to an input of the memory to disable the memory input from responding to spurious signals during a power-down condition.