Blu-ray or Blu-ray Disc (BD) is a digital optical disc data storage format. It was designed to supersede the DVD format, and is capable of storing several hours of video in high- definition (HDTV 720p and 1080p ) and ultra high- definition resolution ( 2160p ). The main application of Blu-ray is as a medium for video material such as feature films and for the physical distribution of video games for the PlayStation 3, PlayStation 4 and Xbox One. The name "Blu-ray" refers to the blue laser (actually a violet laser ) used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs.
The plastic disc is 120 millimetres (4.7 in) in diameter and 1.2 millimetres (0.047 in) thick, the same size as DVDs and CDs. Conventional or pre-BD-XL Blu-ray discs contain 25 GB per layer, with dual layer discs (50 GB) being the industry standard for feature- length video discs. Triple-layer discs (100 GB) and quadruple-layer discs (128 GB) are available for BD-XL re- writer drives.
High- definition (HD) video may be stored on Blu-ray discs with up to 2160p resolution (3840×2160 pixels) and at up to 60 frames per second. DVD - Video discs were limited to a maximum resolution of 480p (NTSC, 720×480 pixels) or 576p (PAL, 720×576 pixels). Besides these hardware specifications, Blu-ray is associated with a set of multimedia formats.
