The HD DVD is a digital optic data storage media format that uses a 120mm diameter disc. A single layer HD DVD has a storage capacity for 15GB data, as compared to a 4.7GB of a standard DVD. A dual layer HD DVD can store 30GB data, while a triple layer HD DVD has a 45GB capacity. The HD DVD is complemented with the HDTV or high definition television. A high definition television is a system that scans pictures with more than double the lines of resolution as compared to a standard format television. Therefore, equipped with 1,080 lines of resolution, in contrast with 480 lines for regular television and DVD players, it provides a very superior quality, high definition picture. Most of the HDTVs are wide screen to eliminate the letterbox effect and better viewing.
Structure
The HD DVD optical disc has two 120mm diameter substrates bonded back-to back, each having surface layer thickness of 0.6mm. Its optical pick-up heads numerical aperture is 0.65 and its information is read using the blue-violet laser of 405nm wavelength. The use of a shorter wavelength in an HD DVD enables a small spot size of the laser to be maintained. This allows for lesser diffraction and data to be read from a high density on the surface of the disc. The higher density of data storage on an HD DVD results in higher capacity for data storage.
Quality Attributes
The HD DVD provides a high quality audio output and high definition picture quality as compared to any other existing media. This has a much higher capacity for data storage within a single disc; 15GB for single layer, 30GB for dual layer, and 45GB for triple layer format. Owing to the use of latest compression technologies, a 15GB disc has adequate space for a whole two hour movie in HD quality plus bonus content such as extra scenes, directors comment, a documentary about the movie, and space to spare. A 30GB disc can store eight hours of HD images (1,125 lines) or 48 hours of SD images. The HD DVDs are rewritable in format and are therefore able to write, erase and re-write data, enhancing its utility many times over.
The commercially available HD DVDs are equipped with an in-built copy restriction technology developed by AACS LA (Advanced Access Content System License Administrator). A Audio Watermark Protection has also been devised for the HD DVDS. These water marks are made by altering the audio waveform in such a manner, that they convey a digital code. These audio codes are not recognizable by the human ear, but can easily be neutralized by audio editing software or an HD DVD player. This means that the DVD players are equipped with a sensor that can pick up inaudible water-marks in the sound track of the movie being played back.
The HD DVD player will be able to discern whether the disc is an original or a copy. If a copy is detected, the player will refuse to play the disc. Another technique is that of a water mark for home entertainment that differs from that of the cinema mark, which the player can identify to check whether the DVD is legitimate or an illegal copy.
The data processing in the HD DVDs is carried out with almost negligible noise. The noise problems caused by playing of other high density media are avoided in the HD DVD players by use of the latest in signal processing, and use of PRML (Partial Response Maximum Likelihood).
The excellent quality of data compressing in the HD DVDs helps achieve high quality digital image replay. The regular DVDs use MPEG-2 format for data compression, which allows for almost one third of the data compression possible through the HD DVD. Use of MPEG-4 AVC and VC-1 which are based on Microsofts Window media, allow for greater compression efficiency and high quality replay.
The HD DVDs provide a data transfer rate of 36 Mbps, much higher than the 24 Mbps, which is the maximum for digital TV broadcasts. This simplifies recording and play back of high definition images for hours of viewing.
The HD DVD disc is very sturdy and does not need any protective cartridge. This can simplify its use in slimmer drives and with just a single lens optical head. The HD DVDs are priced based on their features and brands. A Toshiba HD A1 DVD player costs $500, and an HD XA1 DVD player costs $800, while the Samsung players range from $140 to $250.
Technical Advantage
The HD DVD discs and the original DVD discs are very similar in structure and format. They are both built using 120mm diameter substrates of 0.6mm thickness, bonded together back-to-back. Although they are read using different optical diodes, the dual laser sources can be incorporated within a single machine. The similarity of structure was deliberately retained keeping in mind the convenience of using a single play back medium for the old DVDs and the newer HD DVDs. This has been extremely advantageous for the disc and player manufacturers, since incorporation of the new HD DVD needs only minor modifications on the existing DVD technology.
There will be backwards compatibility available for all HD DVD players, allowing the consumers to purchase a single player for playing both the HD DVD and the DVD discs. The DVD manufacturing companies can continue to use their current production facilities with incorporation of minor alterations for changing over to HD DVD production. The single-lens optical head has a structure that allows for incorporation of the dual red and blue laser diodes within a single, compact HD DVD player.
The HD DVD standards, being similar to DVD standards, have simplified an early and cost-effective disc and hardware production. This will assure a high quality product at affordable prices and with widespread availability.
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