The Audi A4 is a line of compact executive cars produced since 1994 by the German car manufacturer Audi, a subsidiary of the Volkswagen Group. The A4 has been built in five generations and is based on the Volkswagen Group B platform. The first generation A4 succeeded the Audi 80. The automaker's internal numbering treats the A4 as a continuation of the Audi 80 lineage, with the initial A4 designated as the B5-series, followed by the B6, B7, B8 and the B9. The B8 and B9 versions of the A4 are built on the Volkswagen Group MLB platform shared with many other Audi models and potentially one Porsche model within Volkswagen Group.[3] The Audi A4 automobile layout consists of a longitudinal engine front-engine design, with transaxle-type transmissions mounted at the rear of the engine. The cars are front-wheel drive, or on some models, "quattro" all-wheel drive. The A4 is available as a sedan and station wagon. The second (B6) and third generations (B7) of the A4 also had a convertible version, but the B8 version of the convertible became a variant of the Audi A5 instead as Audi got back into the compact executive coupé segment.