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CED Digest Vol. 3 No. 17  •  4/25/1998


From: "Ed Ellers" 
To: "Tom Howe" <>
Subject: Re: CED Digest Vol. 3 No. 16
Date: Sun, 19 Apr 1998 14:46:35 -0400

Jesse Skeen wrote:

"I heard the 1981 Sears Catalog had a laserdisc version sent to those who
had their players registered (And I'd eat dirt to have one of these!) but
that's about it on the consumer end."

That was a seasonal sale catalog -- *not* the big "Wish Book" -- and was
only issued on disc for one region (those catalogs vary by region, and they
didn't want to do more than one disc).  I've seen this; a dealer in
Louisville got hold of one and used to use it to demo LD players.

"Oh well, those CD-V's (audio CD's with 20 minutes of audio only then on the
outer part 5 minutes of analog CLV video with digital sound (no analog
track) would've make neat sales tools, but that format never caught on."

The format didn't, but nearly all CD/LD players will play CDV singles so
it's not a matter of incompatibility.  Actually the singles were popular for
a while in Japan, but with only the video portion (no CD audio section).

Date: Fri, 24 Apr 1998 11:28:47 -0700
From: Neil Wagner 
To: *CED Digest <>
Subject: Videodisc History Part 23

>From the August 1982 Popular Science -

Optical disc can store an encyclopedia - Part 2
                   by John Free
New recorders capture images, computer data,
or audio for instant playback

[Part 1 of this article appeared in the
 previous issue of CED Digest.]

Terabyte Memory
  Mass storage with optical digital discs involves huge
numbers.  An optical disc can store about 50 billion
bits per side.  (A common data-storage term, the byte,
requires eight bits, or the memory space for one alpha-
numeric character.)  International Resource Development,
Inc., a Norwalk, Conn., consulting firm, recently con-
trasted the capacities of optical discs with conven-
tional storage.  Costs and quantities needed for storing
100 billion bits of data are compared:

  Medium           Quantity                     Cost ($)
Magnetic disc    80 200-megabyte packs           40,000
Computer tape    90 tapes (2400', 6250bpi, 8trk)  1,350
High-density mag tape       2400' (2-in. tape)      100
Optical disc     One 12-inch disc                    10

  The $10 cost of an optical disc is projected.  Actually,
only one firm at this writing is marketing optical discs.
Drexler Technology (Mountain View, Calif.) charges several
thousand dollars for its evalualation discs.  The low price
is foreseen with full-scale production in the mid-1980's.
  Hard magnetic discs are stacked for compactness and read
with multiple heads for fast access to data.  Manufacturers
of optical-digital-disc sytems are devising jukebox-like
packages, too.  An optical scanner for each disc surface
ensures split-second playback of data.  Such stacked optical
discs make campact terabyte (trillion byte) storage memories
feasible.  About 1000 optical discs should be able to store
the contents of the National Archives.

Video vs. digital
  While the technology going into optical discs is similar to
that used for optical videodiscs, there are several important
differences.  The videodisc standardized by N.V. Philips and
MCA starts with a glass master disc.  A video signal, like
that broadcast from TV stations, switches a sharply focused
laser beam on and off.  A spiral pattern of pits that vary in
length is created on the master after processing.
  Additional steps provide metal discs used to stamp out the
plastic Laservision copies sold in stores.  During the produc-
tion process, a speck of dust bigger than the micron-size
(millionth of a meter) pits can contaminate a disc.  In optical-
disc players, a laser beam reflected from the spiral disc tracks
creates light pulses of varying duration.  The highly reflective
metal area between the pits produces these pulses.
  That dust speck can screw up the video signal briefly.  You
might see it as a black scan line in the picture.  The light
flashes from the disc surface are actually decoded as a fre-
quency-modulated (FM) signal by the player's electronic circuits.
  Now contrast the requirements and technology for an optical
digital disc.  The disc surface might have a thin coating of
tellurium, an element that melts at relatively low temperatures.
A solid-state laser in the recorder-player can deliver 50-mW
bursts of light to melt pits in the metal.  The signal to create
these pits is in an on-off digital format, more condensed than
video signals since it requires only the presence or absence of
a short pit on the disc.
  The signal encoding these pits mught be a TV picture of a 
photo from an encyclopedia.  In that case, a speck of dust on
the disc might create an acceptable if irritating glitch in
the picture.  For computer data--say, a satellite-transmitted
update of your credit-card records--however, that dust speck
or micron-size blemish on the disc would be disastrous.
  To avoid data distortion, optical digital recorders use an
error-detection technique.  Philips, a pioneer in both video
and digital optical discs, calls its monitoring method "DRAW"
(direct read after write).  Before it is encoded with data,
part of the laser beam used to "burn" pits into a disc is
split off.
  This second beam can be used to monitor what has just been
written on the disc.  By comparing this data with the original
information, errors are detected.  Another section of the disc 
can then be used to store the data again, and the computer
keeping track of everything is programmed to "forget" the bad-
data section.
  Research is also under way to find reliable techniques for
storing digital information on videodiscs.  For this, the digi-
tal data might be encoded on a video signal before storage.
This simplifies mass production.

[Part 3 of this article will appear in
 the next issue of CED Digest.]

Neil -

From: "plc" 
To: <>
Subject: belt size for sgt100?
Date: Fri, 24 Apr 1998 15:02:47 -0500

Hi, I need to know what size the belt that pulls the turntable
on the SGT100 is?  I found a player but it has no belt, not even
a broken one.  can you help?


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