Heres a little info from howstuffworks.com
Best of Both Worlds
Volkswagen has recently released a "Twincharger" engine on a Golf GT. The Twincharger comes with both a supercharger and a turbocharger. At low engine RPM, the supercharger blasts air into the cylinders to enhance low-end torque. At high RPM, when exhaust gases have been produced in sufficient quantity, the turbocharger kicks in to increase top-end performance. The GT, which is available only in Europe, hits 62 miles per hour in 7.9 seconds. It can also reach 136 miles per hour while still delivering 39 miles per gallon.