I’m not sure how I missed it when it came out in 2009, but Peter Norris has put together an absolutely fantastic write up on the internal structures of the Registry. Deep internal knowledge like this is vital when you are finding parts of old registry files in unallocated space, the page file, or memory. For anyone else who has seen this paper, it is hosted here:
http://amnesia.gtisc.gatech.edu/~moyix/suzibandit.ltd.uk/MSc/