Blue ray discs came about in 2006. They have a high storage capacity which means they can store hours of high defintion audio and video. Because high definition needs more storage standard DVD's blue ray give you the ability to store high definition files and still have spaces for add on and extras.
HOW THEY WORK?
Blue rays not suprisingly use a blue laser to scan the digitally encoded which is found in the spiral grooves that run from the centre of the disc to the edges. The blue laser has a shorter wavelength compared to the normal red laser therefore can focus more precicsily. There for the 'bumps' can be smaller meaning more data can be encoded.
The blue ray disc has a polycarbonate layer which means the data is the top layer the prevents read-a-bility problems that normal DVD's faced. The recording layer sits closer to the reading lens which can also prevent disk tilt. Because the data is on the top layer a hard proof is used to protect the data from fingerprints and scratches.