Patent ID: 8611198

Claim:
A method for distinguishing a given multilayer optical disc comprising the steps of: (X) determining what group the multilayer optical disc that has been loaded into an optical disc drive belongs to by a group determination method, the group determination method comprising: (A) measuring either a distance from a first one of multiple information layers of the given multilayer optical disc to a second one thereof, which is located adjacent to the first information layer, or a distance from the first information layer to the surface of the optical disc; and (B) determining, by the distance measured, what group the given multilayer optical disc belongs to, wherein at least one of the multiple groups comprises different types of multilayer optical discs which have different amounts of information layers from each other; and (Y) irradiating one of the information layers of the multilayer optical disc and determining, by the light beam that has been reflected from the information layer, how many information layers the multilayer optical disc has after the step (X).