How Burners Work:

Blank CD or DVD media has a smooth reflective metal layer, which rests on top of a layer of photosensitive dye.

As a blank disc , the dye is translucent and light can shine through and reflect off the reflective metal surface. With concentrated a laser of a particular frequency, the dye layer is heated and the dye then turns opaque and will not allow any further light to pass through.

This process is achieved by using a CD or DVD burner. The burner moves in exactly the same way as a reader does. It moves outward while the disc spins. The bottom plastic layer has grooves pre-pressed into it, to help guide the laser along the correct path. To burn the disc, the burner simply turns the laser writer on and off in synch with a specific pattern.

Once a disc is burned, you can no longer burn to that space that is been written to nor can it be erased. As technology has progressed, some burner technology will allow to add to a disc as long as you have not written out the session on the previous burn.