Unless you have been living in a hole for the past 3 months, you probably know:
*Competing HD DVD and Blu-Ray hi-def DVD formats both use Advanced Access Contest System (AACS) in order to protect their data from unathorized replication.
*The Blu-ray format also has announced an additional layer of content protection called “ROM Mark”.
Up till now, what “ROM Mark” actually means has been something of a mystery. Well, wonder no more. Here’s a nice summary of the info in several ROM Mark-related patent applications.

It looks like ROM Mark is aimed at simply determining if a disc has been pressed from an authorized master. That’s it. So AACS is control on the client side, and ROM Mark is control on the distributor/duplication side.