"Don Pearce" wrote in message

On Thu, 21 Jun 2007 09:14:41 +0100, Jim Lesurf
wrote:

In article
, Arny
Krueger
wrote:
"Jim Lesurf" wrote in message



IIUC The BluRay system differs from both standard DVD
and HD-DVD in locating the information layer much
closer to the disc surface. Just 100 microns below the
read surface, rather than around 600 for other discs.

IME the most common kind of scratching that puts an end
to the usefulness of a DVD does not come from the read
surface side, but from the label side.

That may be so. I've not encountered any problems with
DVD as yet. In general, it seems to me to be physically
about as robust as CD.

However IIUC with DVD the information layers are roughly
half-way though the disc - i.e. about 500 to 600 microns
from either surface. But with BluRay they are only
around 100 microns from the playing surface, and over a
mm from the label surface. Thus I am wary of assuming
that BluRay will behave as DVD in terms of vulnerability
to scratches or dirt.

There is a significant difference in the hardness and scratch-resistance of
the two layers of plastic on either side of the information layer. One is
polycarbonate, and the other is dried acrylic lacquer.

The biggest difference in vulnerability to scratches is the size of the
features of the disc that carry the information.