Closed information system with physical copy protection.

摘要

An information system comprises a record carrier (1) and a playback apparatus. Information have been recorded on the record carrier (1) in the form of variations of a first physical parameter. The playback apparatus scans the record carrier by means of a transducer (41) which is responsive to said variations of said first physical parameter. An information recovering circuit (42) recovers the information from a detection signal received from the transducer (41). The record carrier (1) exhibits a second variation of a second physical parameter, which differs from said first physical parameter but which is of type that is detectable by means of said transducer (41). A detection circuit (43) detects the a presence of the second variation on the basis of a detection signal received from the transducer (41). A circuit (44) responsive to the detection means enables the information recovering circuit (42) in the event that the presence of said second variations is detected. Copying machines of usual types only copies the variations in physical parameters which represent the information without copying the variations of the second physical parameter. The information on copy obtained by means of such copying machine can not be recovered. So copying of record carriers is made less easily. <IMAGE>