So what's the fuss about this new Blu-ray format? First, capacity has been increased from the present 8.5GB limit on dual layer DVDs to a whopping 25GB for a single layer Blu-ray. Dual layer Blu-ray discs are double that capacity at 50GB. This is done by the use of blue laser diodes (hence the name), which have shorter wavelengths compared to the red ones used in current DVD technology. This results in greater data density, since the blue laser can be focused on a smaller area. It's like writing with a finer pencil; you can simply write more given the same sheet of paper. That's the abbreviated version of how Blu-ray has greater capacity over the DVD and should be all the information a casual user needs to know. You can refer to this informative entry on Wikipedia for its origins back and all the developments since if you prefer the long version.



Link: HardwareZone