Special Coverage: Blu-ray

What Is Blu-ray?

Blu-ray was developed by the Blu-ray Disc Association (BDA), a consortium of companies that includes Panasonic, Pioneer, Samsung, and Sony, among others. Unlike HD DVD, Blu-ray was never submitted to the DVD Forum, an industry association that is responsible for all things DVD. Nevertheless, Blu-ray enjoys the support of almost every relevant consumer electronics company and seven out of eight major movie studios (some of which are straddling the fence by releasing HD DVD titles as well). Interestingly, LG and Hewlett-Packard were originally staunch supporters of Blu-ray, but both companies recently shifted their position to neutrality.

As with HD DVD, there are three flavors of Blu-ray: BD-ROM (read only), BD-R (write-once), and BD-RE (rewritable). The technical details of the format are best summarized in a table DVD vs Blu-ray Specs.

DVD, HD DVD, and Blu-ray are implemented on discs measuring 12 cm in diameter and 1.2- mm thick, but that's where the similarity ends. Blu-ray was designed to maximize capacity and performance using a different disc structure than DVD. By contrast, HD DVD was designed to be as compatible with the DVD manufacturing infrastructure as possible.

For example, the top surface protecting the data layer of a Blu-ray disc is only 0.1-mm thick; the rest of the disc is used as substrate to support the data layer.



As a result, Blu-ray discs are one-sided only, with one or two data layers in the current spec. (In the future, it will be possible to include more layers; research labs are now working on prototypes with up to eight layers.)

The data capacity of Blu-ray is 25 GB per layer, which is 67 percent more than the 15-GB per layer offered by HD DVD. How can Blu-ray offer so much more capacity? By using a smaller track pitch (the distance between consecutive turns of the spiral data track) and pit size (the indentations that represent data within the spiral track) as well as a more tightly focused laser beam.

Blu-ray players use a pickup riding just 0.5 mm above the disc surface, which is much closer than the 1.7 mm used for DVD and HD DVD. However, most Blu-ray player manufacturers maintain that their pickup mechanism is completely compatible with DVD and CD (though some devices will not play CDs due to design decisions), and it can be incorporated into slim-line drives for laptop computers, such as thesoon-to-come Sony Vaio, which includes a Blu-ray read/write drive.

With the lens riding so close to the disc's surface, some claim that Blu-ray might be too sensitive to fingerprints, dust, and scratches. According to the BDA, there is no cause for concern thanks to various coating technologies. For example, TDK's Hard Coat process deposits on the disc's surface a layer of very hard, optically clear material that is essentially impervious to scratches, fingerprints, and other marks.



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