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I/O Metric - the disc lost to time
https://forum.lddb.com/viewtopic.php?f=14&t=10625
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Author:  greenlaser [ 18 Nov 2022, 03:07 ]
Post subject:  I/O Metric - the disc lost to time

I am reading "Revolutionary Technology: an introduction to the video and digital audio disc" by David K. Matthewson.
I was surprised to learn about the following! In the mid-1970s, an American company called I/O Metric Corporation created videodiscs which could be reproduced photographically:
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The author says it demonstrated all of the benefits that laser videodiscs have. However, the I/O Metric system vanished without a trace. I could only find one mention of I/O Metric Corporation on Google. They worked with the US NOAA in 1974 on an atmospheric analysis system. Has anyone heard of I/O Metric before?

Author:  greenlaser [ 01 Dec 2022, 20:06 ]
Post subject:  Re: I/O Metric - the disc lost to time

I found more information! The creators published an article in the Journal of the SMPTE, 1974. I was able to get a digital copy from a library. Here is what I know:

  • the master used ordinary silver halide film
  • duplication of the master could be done through simple contact printing
  • multiple layers could be sandwiched together for greater capacity (like DVD/Blu-Ray does)

  • for playback, the disc could be illuminated by white light (no laser needed)
  • the disc had ~7Mhz bandwidth. The limiting factor was how fast they could modulate their recording laser
  • a video signal could be recorded directly without using a carrier (no FM needed). They called this the "analog mode"

  • copies: a silver halide copy could be made by use of an internegative
  • alternatively, a diazo copy could be made directly, without an internegative.
  • "diazo materials are significantly less expensive than silver emulsions"
  • such copies were "essentially indistinguishable" from the master

  • at least 4-layer sandwich discs were possible (an micrograph shows a 4-layer disc)
  • both CAV and CLV recording were possible. One layer held 14.1 minutes of video at CAV. CLV "yields an increase in playing time of about a factor of two".
  • speculation: with four CAV layers, could you fit ~113 minutes on a disc? (14.1 * 2 * 4)

The claimed advantages of the system were "archival image quality, ease of duplication, and low cost".
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