What does the centre diff do and what is the front to rear wheel ratio bias on a UK Turbo 50/50?, are other models different?

Does the centre diff transfer power to either the front or rear, so say if your rear wheels were on ice, would the centre diff transfer all the power to the front? Or is it not as complicated and this and simple restrct is to say 50/50?

Thanks

 

Google is your friend, look up vicous differentials

Tony