Servo positioning system for magnetic disk file

Claim 1

APPARATUS FOR CONTROLLING THE POSITION OF A MAGNETIC TRANSDUCER RELATIVE TO A SELECTED ONE OF A PLURALITY OF DATA TRACKS OF BINARY BITS RECORDED ON A MAGNETIC RECORD MEDIUM AND WITH WHICH SERVO CONTROL SIGNALS ARE DERIVED FROM THE BINARY BITS IN THE SELECTED DATA TRACK, COMPRISING A PAIR OF READ ELEMENTS IN SAID TRANSDUCER, THE EFFECTIVE WIDTH OF EACH ELEMENT BEING LESS THAN ONE-HALF THE WIDTH OF A BINARY BIT, SAID READ ELEMENTS BEING ALIGNED AND SEPARATED FROM EACH OTHER IN A DIRECTION NORMAL TO THE LENGTH OF SAID TRACKS, SUCH THAT BOTH ELEMENTS READ THE SAME BINARY BIT SIMULTANEOUSLY, EACH OF SAID ELEMENTS INCLUDING COIL MEANS HAVING A SIGNAL GENERATED THEREIN BY EACH BINARY BIT IN RESPONSE TO RELATIVE MOVEMENT BETWEEN SAID MEDIUM AND SAID TRANSDUCER, MEANS FOR COMPARING THE SIGNALS GENERATED IN SAID COIL MEANS TO PRODUCE AN ERROR SIGNAL WHICH IS A FUNCTION OF THE DISPLACEMENT OF SAID TRANSDUCER FROM THE CENTER OF THE ONE TRACK, AND POSITIONING MEANS RESPONSIVE TO SAID ERROR SIGNAL FOR MOVING SAID TRANSDUCER TO POSITION IT OVER THE CENTER OF SAID TRACK.