A field-effect transistor flip-flop and three lines coupled through other field effect transistors to the flip-flop for permitting information to be read from and written into the flipflop nondestructively and for producing, in response to a voltage indicative of a tag bit applied to one of said lines, a signal indicative of a match or mismatch on another of said lines. The invention described herein was made in the course of or under a contract or sub-contract thereunder with the Department of the Air Force.