Blu-ray Disc (BD) is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Conventional (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 layers (128 GB) are available for BD-XL re-writer drives.
Just as DVD meant a five to ten time increase in storage capacity compared to CD, Blu-ray Disc will increase DVD capacity by five to ten times. This is due to the usage of a blue instead of a red laser and improved lens specifications, allowing for a much smaller focus laser beam which enables the recording of much smaller and higher density pits on the disc.
Due to the fact that the data layer on a Blu-ray Disc is placed much “closer” to the laser lens than in DVD, there is less distortion resulting in significantly improved tolerances. Hence, more precision and ultra high storage densities are made possible.
|Type||Diameter (cm)||Layers||Capacity (GB)|
|Single layer, standard size||12||1||25|
|Dual layer, standard size||12||2||50|
|XL 3 layer, standard size||12||3||100|
|XL 4 layer, standard size||12||4||128|
|Single layer, mini disc size||8||1||7.8|
|Dual layer, mini disc size||8||2||15.6|