Geek Speak — HabitableZone

Geek Speak » in reply to HD-DVD versus Blu-Ray

wavelength?
Robert — (archived)

It's true that the basic architecture of all the disks is spiral/phonograph style, and you'd think that the system with the highest track density could accommodate the others as a subset. Unless the ratios happened to be inconvenient i.e. non-integral.

Just speculating, but I'd bet the problem is laser wavelength. They're using blue lasers for shortest wavelength and thus highest bit density, and also in multiple-layer discs using coatings tuned to be transparent to particular wavelengths. On a double-layer disc, the first pass reads the top layer at one frequency, the second pass at another that passes through the top coating and reads the bottom layer. If their materials are different and thus require different lasers, a multiformat player would have to carry around four sensor sets instead of two on the head mechanism. Or maybe three at a minimum, if the top coat can be read by a single laser.

Not insurmountable, probably, but a considerable complexity that would add cost. Or so I guess.

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