CD+DVD: how does it work?

Factual Questions
1

This entertainment product (warning: Flash site) claims to be a DVD on one side and a CD on the other. Now, I’m slightly familiar with the technology, and I understand that DVDs can have different layers, so I can see a DVD player being able to “ignore” the CD side.

But how does the CD player handle the situation? Is the “focus” of the laser set such that it doesn’t really matter what else there is on the disc so long as there’s CD information at a given depth on the disc? I was under the impression that on a standard audio CD, the “information” was pretty close to the label, depth-wise. How would this be possible when the disc is pulling double duty as a DVD? Is there some sort of material sandwiched between the DVD side and the CD side so that neither player will “see” the other side? At this point I’m just making shit up so someone please set me straight.

2

imagine gluing a CD and a DVD back-to-back.

didn’t look at the site, but:

CD’s and DVD’s are pressed (just as records used to be) of the same (AFAIK) material.

yes, you could press a CD image on one side of a blank, and a DVD image on the other.

is that what you are talking about?

3

Well, the product in question has to be the same size and thickness as a regular CD/DVD, so if it really was a DVD and CD smushed back-to-back (presumably with reflective material in between - ?), then each would be half as thick as they usually are. Would this cause problems for the CD player when it is expecting the “information” “deeper” in the disc?

4

Double-sided DVDs are slightly thicker than single-sided DVDs, but they work just fine. The important optical property of the disc is the thickness of the clear plastic between the laser and the pitted metal, it doesn’t matter what’s on the other side of the metal.

5

Ok, I see. So how does a double-layer DVD work?

6

See if this page helps, chriszarate.

7

I would also think this would cause a problem for the CD layer, since the data layer is the very topmost part of the disc…it’s not anywhere in the middle, so it needs almost the entire thickness of the disc as polycarbonate…

8

Ok, now I understand that the two sides are fully independent of each other. But after looking at this page on that site, it seems clear that a CD needs like a millimeter or so of polycarbonate on top of the data layer. If you put a DVD data layer on the other side, it seems almost certain that the width of the disc will be more than 1.2 mm. The DVD player I suppose can handle that, but won’t that cause spin problems for the older technology of a CD player?