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| 120 mm discs | |
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Several 2 GB ML CD-based recorders were developed for release in 2002 (TDK's MLCDRW1000 and Plextor's PX-ML3630), but never came to market. This was largely a business decision influenced by the rapid fall of CD-R/RW prices and the simultaneous rise in popularity of writable DVD technology. Calimetrics went on to work on more advanced DVD and Blu-ray versions of their technology, including a proposal to build a next generation version of Enhanced Versatile Disc (EVD). Calimetrics ceased operations in 2004. TECHNOLOGY To store information onto a physical surface, the data must be transformed into a series of marks, using a code used in CDs and DVDs: Because the edges are positioned on a grid that is finer than the minimum mark size, EFM achieves about 1.5 bits per minimum-mark, even though it is a binary code. MultiLevel recording refers to the use of multiple reflectivity values to encode data onto an optical disc. By using more than two levels, more information can be put into the minimum feature size. The following figure illustrates a MultiLevel code (note: colors are used only to represent differences in intensity): The 8-level code used on the prototype systems is a Convolutional Code , storing about 2.5 bits per data cell. When used on dual-layer DVDs, this code increases the capacity by a factor of 1.9. MultiLevel optical recording is an example of Baseband Pulse-amplitude_modulation . While Non-binary, or M-ary , modulation is common in the Telecom industry, the technique had not been seriously pursued in data storage prior to Calimetrics. Data storage Channels are more challenging in this respect, because the writing process can be very Nonlinear . MultiLevel recording is sometimes confused with ''multi-layer'' storage, in which multiple data surfaces are combined into a single disc. The MultiLevel technique can be applied to each layer of such a system. EXTERNAL LINKS |
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