To report gave some details about how the 200GB disc has been produced. The recording medium used is "bismuth peroxide", which forms bubbles of air when heated sufficiently with a laser light. Since the reflection of the light from these bubbles is different than it's surrounding materials, it can be used to store digital information like CD and DVD pits do.
While it's terrific that a 200GB disc has been produced, this achievement is not without its problems. The density of the bubbles is different than that of a standard Blu-ray disc and there are several other technical issues, so whether or not Blu-ray hardware could even read these discs is unclear.
Source:
Reg Hardware
Written by: James Delahunty @ 1 May 2006 19:11