The term turbo-diesel, also written as turbodiesel and turbo diesel, refers to any diesel engine equipped with a turbocharger. As with other engine types, turbocharging a diesel engine can significantly increase its efficiency and power output. Turbocharging of diesel engines began in the 1920s with large marine and stationary engines. Trucks became available with turbo-diesel engines in the mid-1950s, followed by passenger cars in the late-1970s. Since the 1990s, the compression ratio of turbo-diesel engines has been dropping.