Television Electronic Disc
The Television Electronic Disc (TeD) was an early variety of videodisc. Unlike other videodisc varieties, it was not read optically by a laser, but actually used grooves, similar in theory to those of a gramophone record, though these were much narrower and tighter than record grooves, and read at a much faster rotation speed (1500 RPM). They were read using a pressure pick-up which used a piezo-electric crystal to translate the grooves to an electric signal. 8 and 12 inch discs were used; in the original design 8-inch discs held only 5 minutes of video and 12-inch discs 7 1/2 minutes, but this was doubled by the time the format was actually released. This still required multiple discs even for a TV episode, let alone a feature film.