The differing track pitch of the Blu-ray disc makes its pickup apertures differ, however—0.65 for HD DVD vs. 0.85 for Blu-ray—thus also making the two pickups technically incompatible despite using lasers of the same type. HD DVD discs also have a different surface layer (the clear plastic layer on the surface of the data—what you get fingerprints and scratches on) from Blu-ray discs. HD DVD use a 0.6 mm-thick surface layer, the same as DVD, while Blu-ray has a much smaller 0.1mm layer to help enable the laser to focus with that 0.85 aperture.
HD FTW…
I would much rather have a disc that is more resistant to scratches etc…