Last attempt to explain the differences between Blu-ray Disc and HD DVD

[Big Daddy]

There seems to be a great deal of confusion as to the real differences between Blu-Ray Disc and HD-DVD. The purpose of this thread is to explain the differences between the two formats in a language that is understood by most people.

FACTS:
Wavelength of laser to create CD: 780nm
Pit length on CD: 0.85microns
Wavelength of laser to create DVD: 650nm (Red laser)
Pit length on DVD: 0.4microns
Wavelength of laser to create HD-DVD: 405nm (Blue Violet laser)
Wavelength of laser to create Blu-Ray Disc: 405nm (Blue Violet laser)
Yes, both HD-DVD and Blu-Ray Disc use blue ray laser.

By increasing the density of the pits, the standard 12cm disc could contain more digital data for DVD within the same area. In the development of the DVD, its creators aimed at developing a new format that would be backward compatible.

The high definition format reduces even more wavelength of the laser (from the 650nm of the red laser used in DVDs to 405nm). Reducing the laser’s wavelength to 405nm, results in a blue-violet laser that has a smaller spot size and therefore can read data at a higher density within the same space.

HD-DVD uses 12cm diameter discs that have the same 1.2mm thickness of DVDs and Compact Discs.

Why is Blu-Ray Disc able to store up to 25GB where HD-DVD can only offer a 15GB maximum on that same single-side, single-layer disc configuration?

Sony decided to sacrifice compatibility with current DVD formats in exchange for recording capacity by making modifications to the disc structure.

The recording capacity of an optical disc format is proportional to the laser’s wavelength and inversely proportional to the numerical aperture of the objective lens. It is possible to increase storage capacity by decreasing the laser’s wavelength and increasing the numerical aperture.

Sony increased the capacity 2.5 times by decreasing the wavelength from 650nm, as used in DVD, to 405 nm and then doubled capacity once more by increasing the numerical aperture from 0.60 to 0.85. As a result, a 12cm Blu-Ray Disc can store up to 25GB on the same space a DVD stores 4.7GB of data, with HD-DVD storing 15GB in the same space.

But the only way Sony could use such a high numerical aperture was by modifying the disc structure. Instead of having a 0.6mm disc with 0.6mm protective coating, they developed a 1.1mm disc that uses a 0.1mm protective layer. As a result, both Blu-Ray Disc and HD-DVD have a thickness of 1.2mm, but the internal layers have different thickness.

A Blu-ray disc takes a few seconds more to manufacture than HD DVD, but when you manufacture million of discs per month, the cost difference becomes negligible.

SOURCES:
http://editorials.teamxbox.com/xbox/...e-I-HD-DVD/p1/

http://editorials.teamxbox.com/xbox/...luray-Disc/p1/