Video High Density
Video High Density (VHD) was a fairly obscure videodisc format, based on capacitance (similarly to Capacitance Electronic Disc, but using a different standard). While it was developed and demoed in 1978, it was not actually released as a consumer format until 1983 (in Japan). It was never released in North America.
Discs were read by a diamond stylus which read the disc electronically (there were no actual grooves). Discs had up to 99 randomly accessible chapters, and mastering one required highly specialized technical skills (such as knowing how to insert vertical interval codes into the signal in an interleaved manner). The format was designed for interactive use in such things as video adventure games.
Discs were mounted in caddies so that the user did not need to touch them directly. The discs were two-sided, requiring them to be flipped to play the other side.
VHD was never able to outcompete the various other formats available at the time, so it died within a few years. It remained in use for a few specialized applications such as karaoke for a while, though.
