This article is from the RCA SelectaVision VideoDisc FAQ, by tom@cedmagic.com (Tom Howe) with numerous contributions by others.
The Video High Density system- a joint effort by Matsushita and JVC, was
intended to be introduced shortly after the RCA VideoDisc system. RCA
was somewhat chagrined in 1977, when after demonstrating the RCA
VideoDisc system to a group of JVC technical experts, JVC provided a
counter demonstration of their until-then unknown VHD system. The system
uses a 10" grooveless disc stored in a caddy like the RCA system (VHD is
incompatible with the RCA VideoDisc system). A rather wide diamond
stylus tracks the disc surface with a servo mechanism reading tracking
signals adjacent to the capacitance-encoded signal pits on the disc
surface. Because the stylus force is spread over several adjacent signal
channels, estimated disc life is longer than RCA's system- about 10,000
plays per disc. A $12-million factory was built in Irvine, California to
press the discs, but the system was never marketed in the U.S. The VHD
system was marketed in Japan starting in April 1983, and the system was
launched in Great Britain by THORN EMI in January 1984, targeted at the
industrial market.
 
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