DVD is gaining reputation this day and is expected to take over CD as the main secondary drive role in a few years time. DvD is capable of storing about 4.7-17 gigabytes of data compare to CD which only about 700-800mb of data. It is about 4-7 times bigger. CD and DVD like old classic black disk store data in a tracks which is inperceptible to our eyes. So that it is why we must keep the surface of DVD and CD clean and smooth without any scratches and dusts. Scratches will cause DVD and CD cannot be read while dust will cause the laser to malfunction. 
DVD provides better quality and larger storage than a CD eventhough both of them are made with almost the same materials. The space is so vast that it can store a full length of high quality movie with several soundtracks in a single DVD. The different is the compression technique used in both DVD and CD where DVD compression technique is more complex and precise. There are three types of DVD single, double layer, and double sided double layer. The laser used in DVD is also infra-red laser but with shorter wavelength and of different kind of lens than those of CD.
Blue ray disc uses different technology. Instead of using infra-red laser it uses blue ray laser to store data. Blue ray laser has a shorter wavelength thus making it far more narrow than an infra-red laser. This narrow ray is vital especially when there is a need to save as much space as possible making Blue ray disc a better storage disk than DVD. Due to its short wavelenth and special lens the distant between tracks can be largely reduced. (picutures shown are samples only)
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