The laserdisc was basically the first optical disc format and it targeted the home video market (viewing of Hollywood movies at home) and other video applications such as training videos for institutional and industrial uses, music videos, etc. It was first demonstrated in 1972 and then formally introduced into the marketplace in 1978 by MCA/Philips. It is a read-only format disc or in other words the information is placed on the disc at the time that the laserdisc is manufactured and no other information can be added or removed from the disc afterwards.
There are many other names that are used to refer to this type of laser optical disc. Some of these names are:
This disc was an improvement in video quality over other home video options at the time namely VHS and Betamax. LD offers 425 lines of horizontal resolution for NTSC video compared to 240 lines for VHS video. For further comparisons, a DVD movie has 500 lines of horizontal resolution. These discs also provide random access to different chapters of the movie. This is not available with VHS which requires fast forwarding or rewinding for searching, functions which are significantly slower. Another important advantage of these laserdiscs over videotape is that there is no physical contact between the reader and the media, which decreases wear and tear on the media with continually use.
The structure of the LD is a two sided disc with molded pits in the plastic layer that store the information as is the case for other read-only discs. See this page for more discussion on the storage of information on read-only discs. An interesting feature for laservision discs is that although they use pits to store the information both the audio and video were initially stored in analog form. All other optical discs use the “pits” to store digital information. Later digital audio was incorporated in these laser optical video discs. To complete the disc structure, a metal aluminum layer coats the plastic base and this metal then has a protective coating applied onto it and possibly a label on top. Some discs are only single-sided with the other side simply being a dummy substrate.
The standard size for the laserdisc is 30 cm or close to 12 inches. They basically were produced in two versions such as Standard Play (30 minutes of audio/video per side) and Extended Play (60 minutes of audio/video per side). Most players require flipping of the disc to play the other side, although some two sided players were manufactured. Around the mid-1980s after audio CDs were established in the marketplace, laser video players were introduced that could also play the much smaller CDs. A couple of other laser video disc sizes were also available, a 20 cm or 8 inch disc which can hold 20 minutes per side and a 12 cm disc, known as the CD-V or CD-video disc and can hold 5 minutes of video.
The term laser rot was first associated with the deterioration of laser video discs. Several of the discs that were manufactured, especially the early ones, suffered from corrosion of the metal aluminum layer from atmospheric oxygen and pollutants due to poor protective layer quality, which allowed these oxidizing elements access to the metal layer. Some speculate that the adhesive used to bond the two sides of the laserdisc together is responsible for the metal layer corrosion. Once this metal layer is altered, the videodisc can no longer function as required.
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