Articles: Storage

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Unfortunately for content consumers, all attempts to come to an agreement about introducing only one standard were futile. The negotiations should have been started before the companies made their investments into production. So, the users have to choose between two standards again. There are rumors about universal devices that would support both Blu-ray and HD DVD, but it’s not yet certain whether they will ever be released.

What are the points of difference between Blu-ray and HD DVD? Devices for reading and burning such media make use of a blue (blue-violet) laser instead of a red laser that is employed in older DVD drives. The reduction of the laser wavelength from 650nm to 405nm helped increase the areal density by narrowing tracks and the distance between them thanks to the more accurate positioning of the laser. In the Blu-ray standard the distance between tracks (track pitch) is 0.32 microns as opposed to 0.40 microns in HD DVD. A decrease in the pit length was another consequence of the wavelength reduction.

The thickness of the protective later above the data wafer is different between the formats: 0.1mm in Blu-ray and 0.6mm in HD DVD and DVD. As a result, the laser beam has to pass a shorter distance in a Blu-ray device and can be focused more precisely.

This results in denser data packaging on Blu-ray discs in comparison with HD DVD. Thus, a standard single-layer Blu-ray disc can store 25GB of data as opposed to 15GB on a HD DVD. If there are two layers on the disc, the maximum capacity is increased to 50GB and 30GB, respectively. However, the reduction of the protective layer thickness on Blu-ray media increases the chance of errors due to lesser data protection. A special protective coating Durabis has to be used. It is rumored that the manufacturers are currently developing Blu-ray and HD DVD media with more layers than two. From a technical point of view, the manufacturing of Blu-ray media is somewhat more sophisticated because between HD DVD and DVD there is no fundamental difference.

To satisfy the cinema industry majors who are worried about protecting their commercial interest both media types implement the so-called Advanced Access Content System. However, the AACS has already proven to be not impeccably secure. Hackers have offered methods to crack it. Besides, Blu-ray media support two more protection types: BD+ and ROM Mark. The former technology allows dynamic alteration of the keys and the latter uses a watermark system (a watermark is a special mark of the medium to be recognized by the player).

There are certain differences in terms of read speed. The read speed of 1x equals 36Mbps for Blu-ray and 36.55Mbps for HD DVD. A speed of 1x is sufficient to transfer video/audio content from a HD DVD. For a Blu-ray disc, a speed of 1.5x (54Mbps) is required. To deliver only video content at maximum resolution a data-transfer speed of 40Mbps is necessary for Blu-ray. As I am about to test a Blu-ray-compliant optical drive, I want to remind you that its 1x speed (4.29Mbps) equals 3.3x for DVDs and 29.3x for CDs.

The Blu-ray Disc Association has recently announced that starting from October 21 this year all manufacturers of Blu-ray players will have to meet new requirements and to fully comply with the older requirements which they haven’t done so far. We’ll see at the end of the year what effect this “dynamics” of the format is going to have on the demand. Hopefully, people who buy such devices before this date won’t have any unpleasant surprises.

For today, Blu-ray media have outpaced their HD DVD opponents in terms of worldwide sales and are steadily increasing the gap.

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