Abstract: Data are written as transitions on plural tracks of a magnetic disc by a transducer which travels along an arcuate curve formed by an arm turning about an axis beyond the disc periphery. Transition positions are defined by the phase thereof relative to that of a reference indicator on a track of the disc. To align the transitions along a predetermined arcuate curve, a reference transition having a reference phase is written onto a given track. Other transitions of the second curve are written with a phase shift relative to the reference phase.

Abstract: The transverse position of a magnetic head relative to reference positions defining even and odd numbered axes between concentric adjacent tracks of a magnetic disc is detected. Each track includes plural position determining, longitudinally extending, equal length cells. The cells have magnetic variations which cause the head to respond to variations in cells of a pair of abutting tracks to derive a series of waveforms respectively having first and second like amplitudes and shapes for even and odd numbered cells as the tracks are translated relative to the head. The waveforms for each of the odd numbered cells include successive equal first amplitude pulses of first and second different polarities. The waveforms for each of the even numbered cells include successive equal second amplitude pulses of first and second different polarities. The number of pulses and approximate shapes of pulses for the even and odd numbered cells are the same.

Abstract: The amplitude of signals read by a head from a magnetic disc is controlled. The disc includes plural concentric tracks, each including data and reference zones. Each reference zone includes plural abutting tracks having a first axis. Each data zone includes a pair of abutting tracks having a second axis, with the first axis being displaced from the second axis by approximately one-half the radial width of a track. The head is desirably positioned so it is centered on a data zone and straddles a pair of reference zones. Each reference zone includes plural cells having magnetic flux transitions which cause the head to derive a pair of opposite polarity pulses as the cells move longitudinally relative to the head. The pulse amplitude is a function of (a) the distance separating the head from the disc, (b) the head radial position, and (c) the presence or absence of faults on the disc.