Blu-ray vs. HD-DVD
A single, regular DVD disk has a maximum recording capacity of 17 gigabytes, and that’s only if it’s a DVD-18 disc that is a dual-sided, dual-layered. Unfortunately two hours of HD video, with its data compressed, requires 22 gigabytes of storage space. How then is it possible to get more space onto a single disk?
The way Blu-Ray and HD-DVD disks are able to store so much more data than regular DVD’s is due to a blue-purple laser that has a considerably smaller wave length to read and write data from the disc. Since the laser is smaller, it takes up less space of the disk when recording data, and it’s probably where the company came up with “blue ray” as its company name.
There has been an on-going debate as to which is better, and also a rivalry between the two companies as to which is the best replacement to the older DVD’s. For the capacity category, the result is obvious: Blu-ray blows away the competition. HD-DVD disks have 15 GB maximum capacity per side, while Blu-ray disks offer 25 GB per side.
When a Blu-ray or HD-DVD is being recorded to, the high-powered, blue-purple colored laser burns pits on the disc surface. The areas on the disc that are burned with data are called ‘pits,’ while the areas on the disc that were not burned are called ‘lands.’ When a Blue-Ray or HD-DVD disc is being read, the blue-purple laser comes out and is reflected on the disc surface. When the laser reaches a pit it is reflected back with a lower intensity, while when it hits a land the laser is reflected back with a higher intensity. This is the process how the laser on a Blu-Ray or HD-DVD player can tell if an area is a pit or a land: the intensity of the laser reflected back by a land is higher than the amount reflected by a pit.
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