z Wikipedii:
In contrast to turbochargers, superchargers are not powered by exhaust gases but are connected directly or indirectly to an engine. Belts, chains, shafts, and gears are only a few of the ways this is performed. Most automotive superchargers are positive-displacement pumps, such as the Roots supercharger. Some superchargers are compressors such as World War II piston aircraft engines, to be specific the Rolls-Royce Merlin and the Daimler-Benz DB 601, which utilized single-speed or multi-speed centrifugal superchargers.
A supercharger uses mechanical energy from the engine to drive the supercharger. For example, on the single-stage single-speed supercharged Rolls Royce Merlin engine, the supercharger uses up about 150 horsepower (110 kW). Yet the benefits outweigh the costs: For that 150 hp (110 kW), the engine generates an additional 400 horsepower and delivers 1,000 hp (750 kW) when it would otherwise deliver 750 hp (560 kW), a net gain of 250 hp (190 kW). This is where the principal disadvantage of a supercharger becomes apparent: The internal hardware of the engine must withstand generating 1150 horsepower.
In comparison, a turbocharger does not place a direct mechanical load on the engine. It is more efficient because it converts the waste heat of the exhaust gas into horsepower used to drive the compressor. In contrast to supercharging, the principal disadvantages of turbocharging are the back-pressuring (exhaust throttling) of the engine and the inefficiencies of the turbine versus direct-drive.
A combination of an exhaust-driven turbocharger and an engine-driven supercharger can mitigate the weaknesses of the other. This technique is called twincharging. Some Crossley two-stroke diesel engines even used a triple system. As the exhaust was through ports, not valves, it was necessary to use exhaust pulse pressure charging. A Roots blower supplied air for scavenging and a turbocharger provided increased boost pressure when a high enough speed was reached.