Record Carrier Comprising a Rom Mark and a Playback Device For Retrieving the Rom Mark

摘要

In order to distinguish a duplicated record carrier from an original record carrier a pattern is included in a ROM type record carrier that is oriented perpendicular to the reading direction. During illegal duplication the spatial relationship is disturb which can be easily detected. The patterns can be read out simultaneously by the same single read-out spot by including both patterns within the diameter of the optical spot thus guaranteeing that the read-out patterns are actually still spatially close together. Special patterns can be used that allow an easy detection of disturbances caused by the illegal duplication.