Hitachi showcased playback of a four-layer Blu-Ray disc featuring a capacity of 25GB per layer. The company said that the drive used for reading was a standard Blu-Ray drive, at its booth at the 2007 International CES. There have been other academic reports of creating fourlayer (100GB) or even six layer (200GB) disc media by TDK. Some companies have also showcased playback of multi-layer BD media using test players embedded with a special optical head. But in the current demonstation, Hitachi used a ’standard drive’. Hitachi used an optical disc drive based on the “GBW-H10N” supporting 4x speed BD recording, which Hitachi-LG Data Storage, Inc. announced in July 2006. However, the company made some alterations to the firmware and the optical system inside the head, to make the player compatible with four-layer BD playback. Frontend signal processing (Renesas) and other circuits are the same as those used in the “GBW-H10N.”

Of course, the demonstration did not include playback of video. Hitachi set up a reference system that included a PC, the BD drive connected to an oscilator, tuned to display the HF reading signal and especially the data patterns of the disc, which indicate the BD recording marks. Hitachi said, that developing this technology required a drive capable of detecting which layer to read. The company has not specified how the pickup lens actually detects the readout layer, but reportedly explored a wide variety of methods including a very basic way, in which the pickup lens finds a targeted layer by scanning each layer in order of shorter distance from the optical head.

Quadruple BD capacity could be used for storing Digital Cinema Picture Quality content in the future. For example, a 100GB disc could hold 3.5h hours of 64Mbps video (resolution 4K-2K).