Understanding DVD power calibration checks and problems
The correct amount of laser power needed to write each DVD-R disc varies according to the individual recorder, disc, and environmental writing conditions, so before any write operation, all recorders must do a 15 step power test to determine the optimum power for writing to the DVD; this is called "Optimum Power Calibration"(OPC). This whole process is controlled by the recorder, and is initiated by programs such as Nero or other disc writing applications.
The process is accomplished by writing test patterns in the Power Calibration Area (PCA), located on the inner part of the DVD, at different laser powers and reading them back to look for the differences (asymmetry or beta) between the lengths of pits and lands. A DVD-R disc's PCA accommodates 7,088 discreet calibrations.
The power setting responsible for the desired amount of beta is then established as the needed recording power for the disc. All the information acquired during the OPC operation is written for future reference in the disc's Recording Management Area (RMA).
The DVD specification also recommends the use of Running Optimum Power Control (Running OPC) to help ensure that the proper recording power is used across the entire disc.
Running OPC's ability to deal with variations in hardware and media (as well as dust, scratches, and fingerprints on discs) plays a critical role in ensuring data integrity. If you receive a "Power calibration error" error message the cause will be either poor media, poor power, or a defective recorder.
One micometer corresponds to a length which is one-millionth of a meter, A human hair is said to be about 50 micrometers wide.
