LaserDisc (LD)

Optical media evolved from the LaserDisc (a name trademarked by Pioneer). A LaserDisc, developed in the late 1970s, is a 12-inch diameter transparent plastic disk^[1] with data stored as variable-length pits molded into a spiral track on one side. The data side is coated with a thin layer of aluminum to make it reflective. A finished LaserDisc is two such disks cemented together with the data sides in the middle, forming a two-layer disk. Thus, data is read from either side of the finished disk.

A LaserDisc

The LaserDisc was developed as a home entertainment video player. The disks stored analog video and audio using continuously variable lengths of pits in the data surface (not to be confused with a digital system, which would have used pits of two fixed lengths). The video was encoded using frequency modulation in the lengths of the spaces between the pits. The audio was encoded in the length of the pits. Later systems added CD-quality digital sound.

The disks were read by shining a laser through the non-data side to the reflective data side sandwiched between the outer disks. The pits scattered the laser light or otherwise reflected differently than the unpitted part of the surface (the land), allowing the player to extract the data as variable-length pulses (pulse width modulation [PWM]). Data was stored in a spiral track read from the inside to the outside (opposite to a vinyl audio disk).

Early LaserDisc players used helium-neon gas lasers. This limited their life span as the helium gradually escaped from the laser tube, which eventually failed to operate. Once low-cost red LED lasers were developed in the mid-1980s, these replaced the helium-neon lasers in new systems.

In the mid-1980s, Sony developed a LaserDisc format to store digital data. This was used in specialty venues and was rarely seen.

The consumer could not record on LaserDisc as they could VHS and Beta videotape. This led to LaserDisc nearly failing in the marketplace. Its limited success was only due to the development of the Compact Disc, the popularity of which kept the cost of electronic components required for LaserDisc players relatively low.

There are more interesting details about the fascinating story of the LaserDisc, but that format was rarely coupled with computers. If you are interested, you can learn more in the video series, starting with the following video from Technology Connections.