What are Blu-ray discs?
Blu-ray discs (also known as ‘BD’), are a next-generation optical disc format jointly developed by the Blu-ray Disc Association (BDA).
The Blu-ray format offers more than five times the storage capacity of traditional DVDs and can hold up to 25GB on a single-layer disc and 50GB on a dual-layer disc by using a blue laser with a shorter wavelength of 405nm (DVDs use a longer 650nm wavelength red laser and CDs are longer still at 780nm). The shorter wavelength of the Blu-ray system allows the laser to focus on smaller spots and so the pits and spiral groove in the discs can be made even smaller and tighter.
Blu-ray discs are exactly the same physical size as DVDs, CDs and HD-DVD discs at 12cm in diameter and 1.2mm in thickness.
The diagram below shows the difference between single and dual layer Blu-ray discs :
The Blu-ray Disc Association is a group of electronics and media manufacturers that include Apple, Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK and Thomson. The Blu-ray format was developed for the recording, rewriting and playback of high-definition video (HD), in addition to storing large amounts of data.
Blu-ray discs have proved more popular than HD DVD discs as a future replacement for the DVD format.
Below is a diagram illustrating the difference in track pitch between DVDs and Blu-ray discs: