Reading a CD that has no reflective layer
jfoust at threedee.com
Tue Nov 18 08:45:52 CST 2014
At 05:57 PM 11/17/2014, Don Hills wrote:
>I think you're actually more likely to be able to read it in modern drives,
>which are designed to handle lower reflectivity as found on burnt CD-R and
So far, no luck on that front. I think it would require a tweak in firmware.
At 06:07 PM 11/17/2014, drlegendre . wrote:
>Slap a layer of Mylar on the back and give it a shot..? Might even work
>with something of lower reflectivity, like white paper..
Adding a reflective layer to the back was a first and obvious idea,
but upon deeper reflection I don't think it's the right answer.
The pits receive the sputtered aluminum. If adding a backing
layer was the answer, you'd think CD-ROMs would've been made
that way in the first place, as it's easier. It's not a matter
of boosting reflectivity in general, it's about accentuating the
difference between pits and lands.
(I tried Krylon "Looking Glass" spray paint on a couple test discs.
Although this paint does a wonderful job of mirror-izing glass,
it turns out more gray on plastic.)
If the anecdote about early CD drives being able to read non-aluminized
discs is true (and I believe the stories) then it would seem the answer
would be to find a drive that used the old Phillips read heads and
somehow ask it to dump a raw image of the bits it finds, in order
to allow another system to interpret the image. High Sierra wasn't
adopted until late 1986, and ISO-9660 after that.
The CM100 apparently only works on PC and XT era hardware. I saw
mentions on the web that even a 25 Mhz PC is incompatible.
At 02:51 PM 11/17/2014, Mouse wrote:
>I don't understand why this technique was used. Perhaps it's
>easier/cheaper to produce a nonsmooth surface made of a uniform
>material than to produce a smooth surface of a nonuniform material?
I'm not quite sure what you mean here.
Wikipedia has an explanation of the process:
>Is it possible that it's clear only in visible light, with some sort of
>reflective layer present in the (infrared, IIRC) wavelengths used?
The pits surface is normally aluminized and then covered with
some sort of acrylic or lacquer. I too wondered if there's not some
optical characteristic of that boundary that could work like
aluminum. But as you mentioned, detection normally uses the
phase shift, and that's dependent on the frequency of the light.
You'd need to develop an entirely different optical path.
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