Difference between Blu-ray and Hi def dvds?

[warrior4302]

Every time i go to a store that sells DVD'S i notice that theres the normal type then theres blu ray and hi def dvds. I was just wondering what the difference between them is. Also which one is better.

Thanks in advance.

[solbjerg]

Blu-ray use a "blue" laser operating at a wavelength of 405 nanometer to read and write data.
Conventional DVDs and CDs use red and infrared lasers at 650 nm and 780 nanometer respectively.
The shorter wavelenght in blue-ray makes room for more information on the disk. So they are more expensive, but on the other hand, if you buy those with dual layer you can probably have all your information on one disk, unless you have extremely much information on your computer.
Try Wikipedia for more information.
nm=nanometer= 1/10^9 m - that is to say 1 millionth of a millimeter
By the way - do you use milliard or billion in Australia?

greetings

[warrior4302]

Thanks solbjerg,
P.S, we use billion.