I found this article hereand found it quite informative. Very good for a non DP maritime person get a basic understanding of the fundimentals.
I also want to ask exactly how many manufacturers of DP systems are there these days? Not too many years ago, it was Kongsberg, Alstom and Nautronics. Kongsberg is still Kongsberg, Alstom is Coverteam & Nautronics is now L3 plus there are a slew of others who are emerging from behind the woodwork. Who has worked with these systems?