Disc brakes are not a new device, in fact Fred Lanchester designed and patented a disc brake design in the early 1900's pioneering days of motoring before drums became the de-facto standard. It was'nt until the 1950's that disc became popular, first in racing applications in which the D type jaguar was an early adopter,  and then moving to road cars, firstly sports types like the Triumph TR range and the E-type, before becoming standard (on the front) on All cars. The difficulty and extra cost of arranging a parking brake kept them off the rear wheels of most cars for many decades, but now many if not most modern cars use them at both ends.