An analog video format invented by RCA in the late 70's, introduced in 1981 as "RCA SelectaVision VideoDiscs" and technically known as Capacitance Electronic Discs (CED). Although it only had 240 lines of resolution (the same as VHS) this was the first video format to feature letterboxing and the last to be invented and manufactured entirely in the USA.
VideoDiscs are quite similar to records in that playing them requires a diamond stylus to physically ride over microscopic peaks and valleys in the media. The diamond has a titanium electrode on it which reacts to the carbon-loaded disc differently depending on distance, creating capacitance.
The actual discs are housed in square plastic cases. When one wishes to play a VideoDisc he simply inserts the case into the player which removes the disc and ejects the case before beginning to play. A large (usually full color) label on each case identifies which disc it's for and the color of the plastic used to create the case is nearly always indicative of the contents of the disc (although there are only a few colors so these categories are broad). Collectors have found the UPC symbol on the case label to be a reliable method of identifying odd disks and telling similar discs apart.
Between 1981 and 1986 (when disc production ceased entirely -- RCA abandoned the format in 1984) an estimated 1,700 to 2,000 titles were released. Everything from Hollywood blockbusters to industrial training films were transfered to VideoDiscs with an estimated shelf life of 100 years. To play all these discs 44 player models were created by four manufacturers and marketed under 11 brand names.
Technical specifications for the RCA VideoDisc system:
Disc System: CED 525/60Hz NTSC(US) 625/50Hz PAL(European)
Playback System: Mechanical tracking grooved capacitance
Playback Sensor: Diamond stylus with titanium electrode
Playback Time: 60 minutes/side (NTSC)
Video Signal to Noise Ratio: >46dB (CCIR)
Chrominance Signal-to-Noise Ratio: >40dB
Chrominance Bandwidth: 0.5MHz
Luminance Bandwidth: 3.0MHz
Horizontal Resolution: 240-270 lines (magazine reviews)
Audio Signal-to-Noise Ratio: >50dB (USASI), 70 dB (with CX)
Audio Bandwidth: 15KHz
Stereo Separation at 1KHz: 26dB
Dynamic Range Mono: 50dB
Dynamic Range Stereo: 70dB
Audio FM Signal Deviation: +/- 50KHz
Audio Carrier, Mono: 716KHz
Audio Carrier, Additional Stereo: 905KHz
Disc Diameter: 12 inches
Disc material: PVC, carbon-doped
Rotation Rate: 450RPM (525/60Hz), 375RPM (625/50Hz)
Groove Density: 9,541 grooves/inch
Recorded Band: 2.83 inches @ 60 minutes recording
Still Frame Capability: 27,000 frames/side
Raw information and specifications quote compiled from the RCA SelectaVision VideoDisc FAQ at www.cedmagic.com