Well you already now that CD/DVD... are based on a laser, this laser "writes" in the Cd by "marking" it's surface. A laser it's made of light, so it has wave lenght of 750 nanometers, so if you want to have more information in the same space so you need to have a laser with a smaller wave lenght, and it happens that a blue laser has wave lenght of 350 nanometers so you can have twice the information that you had. Plus a blue laser can write dipper in the disk, than a normal laser. A blue laser it's way more expensive since it's laser is produced using a Hydrogen cell (yes Tom is Hydrogen)and other weird components.
This is an easier explanation than the "wave lenght" one: Lets say that you want to park as much cars as you want in a 300m room, so you can park 3.5 m long cars (Blue ray) or 7.5 m long cars (Normal Laser. If you park the "Blue Ray" ones you can park 85.7 cars, and with the traditional laser 40 cars. So the Blue ray can put Twice the information in the same space (Maybe that's why it is called Double Layer). So if you want a 40 GB disk or something you just have to put a Blue ray and a doble layer unit and modify your disk's materials.
Help, my PC with Windows 10 won't shut down properly
Since upgrading to Windows 10 my computer won't shut down properly. I use the menu button shutdown and the screen goes blank, but the system does not fully shut down. The only way to get it to shut down is to hold the physical power button down till it shuts down. Any suggestions?