Gatzet.com

Pioneer has developed a 16-layer read-only optical disc which it claims can store 400GB of data.
The per-layer capacity is 25GB, the same as that of a Blu-ray Disc, and the multilayer technology will also be applicable to multilayer recordable discs. Multi-layered discs have been difficult to develop because ‘crosstalk’ from adjacent layers and transmission loss mean that getting a stable signal from the disc is often nearly impossible.

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