I noticed that MPEG-2 decoder in SP1 is about 30,000 bytes bigger then the
one in the RTM release and that
the description of changes in Vista SP1 contains the following:

". Enhances the MPEG-2 decoder to support content protection across a user
accessible bus on Media Center systems configured with Digital Cable Tuner
hardware. This also effectively enables higher levels of hardware decoder
acceleration for commercial DVD playback on some hardware.
"
I have 2 questions about the above description:

1. What is a "user accessible bus" ?

2. Also I do not understand how increased content protection can
"effectively enable higher levels of hardware acceleration for commercial
DVD playback on some hardware". How is this improvement accomplished and are
what are the pieces of or examples of the hardware on which this occurs?