A wind turbine which is spun by the pressure of the wind acting on the rotor. Old windmills were based on the drag principle: the wind blew against the surface of the blades, causing them to spin. A modern example of a drag turbine is the Savonius wind turbine with a vertical axis. The wind leans against a pair of bowl-shaped blades and thus spins the turbine. Drag turbines generally have a lower efficiency than modern lift turbines but have a simpler design.