Reply #1: Difference in wavelength of laser diode

[hobbit709]

Blu-ray uses a blue light laser which is much higher in frequency, thereby much shorter wavelength. This burns the "holes" that are the bits of data much smaller so that more of them can be put on the same size disk. DVD and CD use red/infrared laser light which has a lower frequency and longer wavelength making bigger holes. This means that instead of 4.5Gb for a single layer DVD, you can put 25Gb of data on the disk. The Blu-ray will read DVD's and CD's just fine. Just means that if you make backups of your data, you won't need as many disks. Hollywood will use it to pack even more coming attractions, added features, etc. on the disk. Your home videos, unless you got enough cash to go for a HD camera will be just fine.