Logical Eccentricity

There is a lot of confusion over the differences between Blue-Ray and HD-DVD, this will hopefully clear some of that up.

HD-DVD:

The biggest difference between HD-DVD and current DVD is the wavelength of the laser that reads the information on the disc. Current DVD use a 650nm wavelength laser, while HD-DVD use 405nm wavelenght laser. This difference in wavelength allows for a great amount of information to be stored on the disc. Despite this difference, HD-DVD player should be backwards with current DVDs; both red and blue diodes can be used with a single lense in HD-DVD players.

HD-DVD has a single layer capacity of 15GB, and dual layer capacity of 30GB. There is a possible triple layer dics that will have a capacity of 45GB. The surface layer of the disc will be 0.6 nm thick. This is the same as current DVDs, meaning the production process will not need to change drastically for HD-DVDs. This thicker layer causes some problems. The laser that reads the data on the disc needs to pass through this layer. As it passes through the layer, the laser gets distorted; thus, each bit of information needs space around, so that the laser can recognize it.

Blu-Ray:

Again, the difference between Blu-Ray and DVD is the wavelength used to read information, Blu-Ray also uses a 405nm wavelength laser. However, there is another crucial difference, the surface layer on a Blu-Ray disc is only 0.1nm thick. This thin layer allows a higher desity of information on each layer; each layer can store about 25GB. Currently four and eight layer dics are being researched, these discs would be able to hold 100 GB or 200 GB of data.

The thinner surface layer creates some problems. First of all, the production process will need to be changed; resulting in higher costs to the consumers. It is predicted that Blu-Ray discs will cost $10 more than current DVDs. Furthermore, since the information is stored close to the surface of the disc, early Blu-Ray discs were very prone to dust and scratches. This problem has been solved with lear polymer coating that gives Blu-ray discs unprecedented scratch resistance. With this clear coating, Blu-Ray dics can be cleaned with just a tissue, apparently can wiststand an attack by a screwdriver. While not required, the Blu-ray Disc Association recommends that Blu-ray drives should be capable of reading DVDs, ensuring backward compatibility.

Technical Comparison

Most of the information in this post is from the Wikipedia

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