Blu-ray Disc

Blu-ray, also known as Blu-ray Disc (BD), is the name of a next-generation optical disc format together developed by the Blu-ray Disc Association (BDA), a collection of the world's most important consumer electronics, personal computer and media manufacturers (including Apple, Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK and Thomson). The format was developed to allow recording, rewriting and playback of high-definition video (HD), as well as storing large amounts of data. The format offers more than five times the storage capacity of conventional DVDs and can grasp up to 25GB on a single-layer disc and 50GB on a dual-layer disc.

While present optical disc technologies such as DVD, DVD±R, DVD±RW, and DVD-RAM rely on a red laser to read and write data, the new format uses a blue-violet laser in its place, hence the name Blu-ray. In spite of the different type of lasers used, Blu-ray products can easily be completed backwards compatible with CDs and DVDs through the use of a BD/DVD/CD compatible optical pickup unit. The advantage of using a blue-violet laser (405nm) is that it has a shorter wavelength than a red laser (650nm), which makes it probable to focus the laser spot with even greater precision. This allows data to be crowded more tightly and stored in less space, so it's possible to fit more data on the disc still though it's the same size as a CD/DVD. This mutually with the change of numerical aperture to 0.85 is what enables Blu-ray Discs to grasp 25GB/50GB.