RAM head positioning and tracking system

摘要

A method and apparatus for positioning and tracking a Random Access Memory (RAM) optical head over an information storage media having a plurality of tracks formed by optically readable deformations ("pits") in the media including, a central controller, a laser diode optical-system carrying head which is movable transversely of the tracks in incremental steps for coarse positioning of the head over a selected band of tracks and a servomechanism which positions the laser's objective lens over a specifically addressed track and maintains it there until another track is addressed. Also discussed is a unique method of generating a tracking error signal as an input to the servomechanism which includes the asynchronous detection of a sector mark and the generation of an independent clocking signal from the synchronous detection of off-track pairs of pits spaced uniformly between other data in the track to produce the tracking error signal.