CDs

Statistics I discussed recently from the Australian Council for the Arts note that digital sales in Australia are set to out do CD sales this year. Interestingly I have been reading a book by an Australian scientist this week (just for a bit of fun) called Great Myth Conceptions in which Dr Karl Kruszelnicki talks about the myth that emerged when CDs were first released, that CDs they were indestructible. Of course we all know that they are sensitive to heat, dust and scratches and that indeed they are far from indestructible.

He does, however, give a very informative run down on how CDs work:

"A compact disc is a 1.2mm-thick disc of transparent polycarbonate (as used in bullet proof glass), with a diameter of about 12 cm. It stores the information in a five-kilometer-long spiral of raised rectangular bumps on the surface. These bumps are about 0.5 microns wide (about 100 times smaller than the thickness of a human hair) and one-eight of a micron high... Because it is virtually impossible to see tiny transparent bumps on a transparent disc a thin layer of metal (usually aluminum, although gold and silver have been used) is laid on top of the polycarbonate. This shiny metal reflects the laser beam, so that it can read the little bumps."

Further Reading
Dr Karl Kruszelnicki, Great Myth Conceptions (2008) http://www.amazon.com/Great-Myth-Conceptions-Temptations-Series/dp/8172237308/ref=sr_1_1?ie=UTF8&qid=1346751440&sr=8-1&keywords=great+myth+conceptions