It is more sportier version of Audi A4, manufactured since 1991. There is 6 different generations of Audi S4, B9 being the current. First generation S4 was based on Audi 100, while the rest of generations is based on A4. In some markets, where Audi RS4 is not available, the Audi S4 is the top tier and highest performing version in Audi A4 family. All S4 versions have permanent all-wheel drive system, and longitudinally mounted engines.