What do the different speeds in Civilization IV do?

Do they slow down production and technology, or do they slow down the passing of time?What do the different speeds in Civilization IV do?
It slows everything, not one or the other.
Both. They slow down everything.What do the different speeds in Civilization IV do?
It depends I think.If you are wanting to go faster then doesn't everything speed up?
they change the passing of timeWhat do the different speeds in Civilization IV do?
im pretty sure it reduces or increases the amount of years or time in between turns