Take the tour ×  I have been recently wondering how is data
stored on and retrieved from optical devices like CDs, DVDs, and
Bluray. What makes these different storage types different from
each other?  share|improve this question Have you checked the
Wikipedia? –  Jellby Jul 19 '12 at 9:01 add comment  2 Answers
On a physical level, they basically work on the same principle
of encoding information in pits arranged in a spiral track on
one or more reflective layers in the disc, and using them to
modulate laser light reflected off these layers. The main
differences are:    1. The size of the pits and the pitch
(spacing between adjacent iterations) of the spiral, with Blu-
ray having the smallest features and CDs the largest.   2. As a
consequence of the above and a phenomenon of physics called
diffraction (which causes light of longer wavelength to be
impossible to be focused into a smaller spot than a minimum
size), newer technologies must use light of shorter and shorter
wavelengths (infrared for CDs, red for