Abstract: A mechanism for moving an access arm carrying a magnetic transducer into the most appropriate position between pairs of consecutive flexible disks in a rotatable disk stack to assure that the proper disk is thereby accessed. The mechanism includes mechanism for preliminarily accessing each of the disks with a plurality of steps between consecutive disks in the stack and filling a position register with a unique identification number from each disk and with numbers of the steps corresponding to each of the disk numbers and mechanism for averaging the step numbers corresponding to each of the disks and placing the average step number in an access table to correspond with each of the disk numbers so that the access arm may be stepped to the step number listed for each of the disks in the access table for a reading or writing action using the transducer.

Abstract: A magnetic disk, particularly of the thin flexible type, has a magnetic head traversing the disk in order to come into registry with various concentric tracks on the disk. An electric motor of the stepping type is mechanically connected with the head for so moving the head, and a "present track number" counter is so electrically connected with the stepping motor as to keep track of the particular magnetic track on which the head is located. On a certain contingency, such as a cessation of power to the system, the circuitry includes components so connected as to cause the stepping motor to move the magnetic head to an outer limit on the disk, outwardly of a prerecorded reference track on the disk. When this point is reached, a switch is actuated by the movement of the head, and connected circuitry causes the head to move back onto the reference track.