An engine configuration with two overhead camshafts per row of cylinders. One camshaft operates the intake valves and the other operates the exhaust valves. This is the usual arrangement in engines with multi-valve cylinder heads. Compared to single overhead cam designs, the direct drive used in all Toyota DOHC engines requires fewer moving parts. It eliminates the rocker arm needed to activate the valves, thus improving efficiency and reducing vibration and noise. Compared to push-rod overhead valve (OHV) engines, which use an arrangement by which the camshaft is located in the engine block and opens the valves via long push rods and rocker arms, it eliminates the need for both of these components. With fewer moving parts, there is less inertia. So, an overhead cam engine can run at a higher speed and produce more power than a comparably sized pushrod engine.