Controlled access dvd

A digital data medium for storing at least one content stream, comprising:

• a set of linked cells including content cells storing stream portions of said at least one content stream;
• means adapted for implementing a read table equivalent which, when correctly set, enables a normal reading of the content cells, i.e. a reading that enables restoration of at least one content stream;
• a data access control module comprising means for positioning a memory in a predetermined state and means, depending on the predetermined state, for authorizing or not authorizing a normal reading of at least one content stream while enabling an access to or a correct setting of the read table;
• the data medium further comprising particular cells that cannot be distinguished from content cells by a device for copying the data medium, at least certain of these particular cells representing a total memory capacity with a first compressibility rate having a value far exceeding that of a second compressibility rate associated with the whole content cells, so that a copy data medium having a capacity lower than the capacity of the present data medium would not have sufficient capacity to store both these particular cells compressed with the first compressibility rate and the content cells compressed with the second compressibility rate, while it would have sufficient capacity to store all the data medium cells compressed with the second compressibility rate.