Counter resetting circuitry for magnetic disk system

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. When a maximum amplitude is detected by the head due to passage over the reference track, the circuitry includes components that reset the content of the 'present track number' counter to zero; and all of the inner tracks within the reference track are counted from the zero count in the 'present track number' counter, so as to thereby compensate for any changes in dimension of the magnetic disk.