Laserdisc

Laserdisc, trademarked under the names LaserDisc and LaserVision, but often abbreviated LD, was the first optical disc recording format commercially available. Invented in 1978, Laserdiscs consistently and significantly under-performed against the VHS format, yet remained on the market until 2001 when DVDs supplanted both it and videocassettes.
Laserdiscs offered superior sound and picture fidelity than VHS or other videocassette formats, and as a result was popular among videophiles. Additionally, because Laserdiscs were read with an infrared laser as opposed to being rubbed across a magnet like a videotape, they would not degrade from repeated playing. The format also had a much greater storage capacity than a VHS tape, allowing for extra features to be put on LD, though fewer extra features appeared on "special edition" LDs, than on later DVD and Blu-ray formats.
Laserdiscs, though moderately popular in Asia, never really took off in either North America or Europe because of the relative expense of both players and discs. Another inconvenience regarding the format was that each side of a Laserdisc could only hold 36 to 64 minutes of analog video and audio (30 to 60 in NTSC regions), depending on whether the recording used constant angular velocity or constant linear velocity. Because of this, viewers typically had to manually eject, flip over, and reinsert the disc partway through a movie, sometimes swapping entire discs in the case of longer movies. Additionally, there was never the possibility of end users actually recording onto blank LDs — a key reason why the VHS and the later DVD formats became popular. One other problem affecting Laserdiscs, particularly on the secondhand market, is their high vulnerability to natural degradation in the form of "laser rot", due to flaws in the manufacturing process that leaves the inner recording layer significantly more vulnerable to the outside elements than a well-made digital optical disc.
== Doctor Who Laserdiscs ==
Despite the somewhat transient nature of the format, some Doctor Who stories were released on Laserdisc. They were sporadically published from 1983 to 1997, though not in every region of the world. For instance, The following chart explains which LDs were released, when, and in which regions. Stories are listed in order of earliest release, irrespective of region.
Serial name 	Episodic format 	UK release BBC/Encore	US release CBS/Fox	Hong Kong releaseUniversal
Revenge of the CybermenRevenge of the Cybermen was also the first VHS and Betamax release.	4 × 25 min. 	December 1983 	N/A 	N/A
The Brain of Morbius 	4 × 25 min. 	July 1984 	N/A 	N/A
Day of the Daleks 	4 × 25 min. (UK) 1 × 89 min. (US movie compilation)	December 1996 	January 1992 	N/A
The Five Doctors 	1 × 90 min. 	N/A 	24 August 1994 	N/A
The Ark in Space 	4 × 25 min. 	October 1996 	N/A 	N/A
Doctor Who (1996) 	1 × 85 min. 	N/A 	N/A 	January 1997
Terror of the Zygons 	4 × 25 min. 	December 1997 	N/A 	N/A
== Footnotes ==
Category:Distribution formats
Category:DVD and video distribution