Hitachi has displayed a prototype of 4 layer Blu-ray disc capable of storing 100GB data at Ceatec 2007 in Tokyo. The best part? Its compatible with already existing Blu-ray players. Reading and writing on 4 layer disc was made possible by stabilizing signal quality and changing the lens focus.

The firm is also working on a 8 layer Blu-Ray disc which can hold 200GB of data. But as the number of layer increase reflection of light decreases which corresponds to a small loss in signal. However by expanding signal (approximately 10 times) the data on the disc can be accessed.

Panasonic has also done some progress in this segment. They have developed a royal purple laser system for Blu-Ray that supports 8X speed. A company spokesman said that the 10,000 RPM speed limits the development to 12X speeds.

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