History of Turbo and the function (From:- www.Rearwheelz.blogspot.com)
Then in 1905, a Swiss engineer named Alfred Bu-chi came up with a replacement for displacement, when he used the exhaust gasses of an engine, to power a compressor that then fed denser air into the combustion chamber. More air meant more fuel could burn, and get more boom. Turbos were quickly adopted by the aeronautical industry. When you're 20,000 feet up, the air is almost half as dense and engines would lose as much as half of their power. 400 horsepower at sea level but moving up to 14,000 feet, it drops to 265. A turbo restored air pressure in the engine back to sea level pressure (This is called turbo normalizing). When a turbo is used to exceed that pressure, that's called turbocharging.