Abstract: A read/write head moves relative to magnetic discs having track addresses corded thereon in Gray code in a plurality of reference zones. The head is moved by an electric motor and reads information as the head is shifted from a starting track to a destination track. The address of the destination track is expressed in weighted, i.e., standard, binary code, and is stored in a register. The address of the head is read by a read element of the head from the recording tracks. In response to the initial and destination tracks, an intermediate track C, approximately halfway between the initial and destination tracks, is calculated. The head is accelerated from the initial track to the intermediate track by feeding a motor for driving the head with a constant current. In response to the head detecting the address of the intermediate track, the current supplied to the motor is reversed so that the head is decelerated. The calculations and comparisons are performed in the weighted, binary code.