Optical memory disc.

摘要

An disc (15) includes a glass substrate on which a plurality of concentric circular guide grooves (or a spiral groove) are formed for the tracking purpuses. A centering plate (13) is secured to the glass substrate (10) in a manner that the center of a circular opening formed in the centering plate is exactly adjusted to the center of the plurality of concentric circular guide grooves (spiral groove). The circular opening (13a) formed in the centering plate is utilized to drive the optical memory disc on a turntable (14). Since the circular opening is not formed directly in the glass substrate, the center adjustment is easily conducted, and there is no possibility that the glass substrate is damaged when the circular opening is formed.