The disc/drum combination is generally found on the rear axle of newer vehicles. It contains the normal components of a disc brake system, but also contains a drum brake within the brake rotor.
Some vehicles have both a disc brake and a drum brake on each rear wheel. The disc brake is hydraulically operated and is used to stop the vehicle when driving. The drum brake part of the assembly is operated mechanically via by the parking brake cable. Drum brake linings should always be checked during routine brake inspections.