professional disc for data (PDD)
Like the Blu-Ray disc and Ultra Density Optical(UDO), the Professional Disc for Data ( PDD) is one of the next generation of magneto-optical storage.
All three disc technologies are incompatible with each other, but they all work with a blue- light laser with a short-wave wavelength of 405 nm and offer many times the storage capacity of DVDs. There is a direct relationship between the wavelength and the storage capacity via the numerical aperture( NA), which determines the maximum focus of the laser beam. Accordingly, optical resolution and thus storage capacity increase with shorter wavelengths and better numerical aperture.
Like the HD DVD, the PDD disc has a diameter of 120 mm, is rewritable up to 1,000 times, uses the phase-change process and has a storage capacity of 20.5 GB in the standard version. The track pitch is just 0.32 µm. In addition, the ratio of overhead data to useful data is significantly improved on the PDD disc compared to DVDs with improved encoding processes. The PDD disc requires about 30% fewer bits than the DVD to store the same amount of user data. The sectors of the PDD disc, like those of the DVD, have a size of 2 KB, but because of the error correction( ECC), 64 KB (32 KB for the DVD) are always written or read.