its complicated.in a nutshell its just a smoother way of engaging the deck functions as apposed to the older,more clunky,chunky way that mechanical decks operate.servo decks are considered superior too as apposed to the mechanical decks,but in my experience when they go wrong they are way harder to fix

az is right about the servo deck on the d8614-one of the nicest to use imho-i love the way the buttons engage with the pleasing sound of the motor....erm...whirring to engage.great sound