Blu-ray Disc

Blu-ray Disc (BD) was developed for home entertainment high-definition video. Blu-ray Disc uses a violet laser with a wavelength of 405 nm (barely inside the visible limit at 400 nm)^[1] that can be focused to a smaller spot than red or infrared lasers. This allows a single-layer Blu-ray disk to hold 25 GiB of data. Up to four layers are possible, giving a capacity of up to 128 GiB.

During its development, Blu-ray competed with a similar format called HD DVD (High-Density Digital Versatile Disc). The main differences between Blu-ray and HD DVD were that HD DVD held 15 GiB (single layer) and that HD DVD had a digital rights management system preventing theatrical movies from being played on computers with HD DVD drives. Theatrical movies were sold on Blu-ray and HD DVD for a short time. However, the Blu-ray format proved more popular, and the HD DVD was withdrawn from the market in 2008.

Unlike CDs and DVDs, Blu-ray disks have no stacking ring. Instead, they have a durable coating that resists scratches. Before this coating was developed, Blu-ray disks came in a plastic cartridge inserted into the drive or player with the disk.

BD-R and BD-RE

Like its earlier counterparts, Blue-ray has recordable and recordable-erasable versions. Recordable Blu-ray disks may have up to four recordable layers and hold up to 128 GiB of data.