There is a tuff competition going on between blu-ray and hd-dvd to occupy the position of being the next-gen format.
The blu-ray format has been founded Sony Corporation and Royal Philips Electronics.
The hd-dvd format has been founded by Toshiba Corporation and Hitachi Corporation.
Both Blu-ray and HD DVD use the same kind of 405nm wavelength blue-violet laser, but their optics differ in two ways. Since the Blu-ray disc has a tighter track pitch (the single thread of data that spirals from the inside of the disc all the way out -- think: grooves on a 12-inch vinyl single vs. an Elvis Costello full-length album with 40 songs), it can hold more pits -- information -- on the same size disc as HD DVD even with a laser of the same wavelength.
THE BLU-RAY READ HEAD
THE HD-DVD READ HEAD
The differing track pitch of the Blu-ray disc makes its pickup apertures differ, however -- 0.65 for HD DVD vs. 0.85 for Blu-ray -- thus also making the two pickups technically incompatible despite using the same type of lasers. HD DVD discs also have a different surface layer (the clear plastic layer on the surface of the data -- the part that collects all your fingerprints and scratches) from Blu-ray discs. HD DVD use a 0.6 mm-thick surface layer, the same as DVD, while Blu-ray has a much smaller 0.1mm layer, which enables the laser to focus at that 0.85 aperture.
The main disadvange with blu-ray is that the thin surface layer costs more which obviously increases the cost of the disc.A special hard coating (Durabis) must also be applied to Blu-ray discs to ensure they're sufficiently resilient to protect the data that's a mere 0.1mm beneath the surface this also drives the cost up.
| Capacity | |||
| Blu-Ray | HD DVD | ||
| ROM single layer: ROM dual layer: RW single layer: RW dual layer: Highest test: Theoretical limit: | 23.3 / 25GB 46.6 / 50GB 23.3 / 25 / 27GB 46.6 / 50 / 54GB 100GB 200GB | Single layer: Dual layer: - - Highest test: Theoretical limit: | 15GB 30GB - - 45GB 60GB |
Comments regarding these formats are welcome.
