In 1931, RCA introduced a new type of record just as movies were beginning to have sound. Motion pictures came on standard-sized reels of 1,000 feet of 35mm film with a running time of about 11 minutes. To match up sound and film, a company called Vitaphone introduced a system that used one of those 3600 RPM turntable motors to rotate a 12-inch disc. To make the audio last the entire 11 minutes of a reel of film, the math said the motor required a gear ratio of 108:1. Divide 3600 by 108 and you get 33 1/3.