MultiLevel Recording

MultiLevel Recording (ML, also known as M-ary) was a technology originally developed by Optex Corporation

Teac and Yamaha

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 Disc 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

EFM

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. By using this code in combination with a smaller mark size and a more efficient error-correction code, the capacity of CD media was tripled. When applied to dual-layer DVD, ML-recording can increase capacity by a factor of 1.9.

MultiLevel optical recording is an example of

signal noise

. ML-drives used sophisticated power-optimization during writing and adaptive equalization during reading.

MultiLevel recording is sometimes confused with

multi-layer

storage, in which multiple data surfaces are combined into a single disc. Multi-layer and multiLevel technique can be combined (as in dual-layer ML-DVD ROM), where ML-modulation is applied to each individual layer of the disc.

References

^ Earman, Allen, "Optical Data Storage With Electron Trapping Materials Using M-ary Data Channel Coding," Proceedings of the Optical Data Storage Conference, SPIE, Feb. 1992, San Jose, California. .

External links

USPTO Link to Optex M-ary patent
"Calimetrics and Philips demonstrate 34GB ML Rewritable System Using Blue Laser". CDRInfo. 2002-09-07. Retrieved 2006-10-24.

[1] Earman, Allen, "Optical Data Storage With Electron Trapping Materials Using M-ary Data Channel Coding," Proceedings of the Optical Data Storage Conference, SPIE, Feb. 1992, San Jose, California. .