The design of the disc varies somewhat. Some are simply solid steel, but others are hollowed out with fins joining together the disc's two contact surfaces. This "ventilated" disc design helps to dissipate the generated heat. Many motorcycle brakes instead have many small holes drilled through them for the same purpose.
Experiments with disc-style brakes began in the 1890s, but the first designs resembling modern disc brakes began to appear in Britain in the late 1940s and early 1950s. They offered much greater stopping performance than comparable drum brakes, including much greater resistance to "brake fade" (caused by the overheating of brake components), and were unaffected by immersion (drum brakes were ineffective for some times after a water crossing, an important factor in off-road vehicles). They have now become standard in most passenger vehicles (though some retain the use of drums on rear brakes).
Carss, motorcycles, and some bicycles use disc brakes.
See also: drum brake