Cmrr Report Number 28, Summer 2007 Introduction

In current HDD’s with disks covered with a continuous magnetic coating, a bit can be written anywhere on the disk. Of course, there is some sanity in the placement of these bits. This sanity is enforced by servo markers and sector headers which define the positions of tracks and sectors. In writing, once the position of a sector and a track are found, the placement of the bits on this track is governed by the write clock. This same clock is used in reading. In reading, variations in the angular velocity of the spinning disk are compensated for by timing recovery and tracking circuitry.