What is the diferent betwen blue streak dik(hd) and a common disk?
Answers: Pretty much everything... well, they are both 12cm within diameter.
Mechanically, the Blu-Ray disc has much, much smaller pits, which are too small to read near the red laser used in the regular player. They use a blue-violet laser, this the "Blu[e]" within Blu-Ray.
The combination of smaller pits and much tighter tracking delivers 25GB on a single lode disc or 50GB on a dual-layer disc, versus 4.7GB on a single layer DVD or 8.5GB on a dual-layer DVD. The pits on a regular DVD are 0.6mm from the bottom... exactly half-way through the 1.2mm disc. The pits on a Blu-Ray disc are 0.1mm from the bottom of the disc (which is also 1.2mm thick). You entail a different lens and laser to read Blu-Ray pits.
Since the pits are so close to the clear side of the Blu-Ray disc, Blu-Ray discs come with a special protective stratum to help prevent scratch.
Both formats are data discs that can convey video formats. DVD-Video officially supports MPEG-2 video and Dolby DIgital or uncompressed audio; open formats include DTS and MPEG-2 layer 2 audio. For Blu-Ray, formats support resolutiions at 1920x1080 60i or 24p within the USA. There are a bunch of next-generation audio formats, and the video can be MPEG-2, MPEG-4/AVC, or VC-1 (derived from Windows Media Video 9)
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