LaserDisc player used to play lecture demonstration videos.
The LaserDisc was the first commercial optical disc storage medium, beginning in 1978, and was the forerunner of CDs, DVDs and Blu-ray. The discs were 300 mm in diameter and were read by a 780nm diode laser interrogating a string of pits and lands in the reflecting surface, with an analogue coding system(http://en.wikipedia.org/wiki/LaserDisc). The discs had a playing capacity of 60 minutes per side.