The MI 79, also known as the Class Z 8100, is a dual-voltage electric multiple unit trainset that is operated on line B of the Réseau Express Régional (RER), a hybrid suburban commuter and rapid transit system serving Paris and its suburbs. The MI 79, designed in the 1970s for the RER B which needed dual-voltage (interconnection) trainsets. They were followed by a derivative version, the MI 84, designed in the 1980s to meet the needs of the RER A line, before reassigned to the RER B in the 2010s.