DVD Drive, External DVD Drives, DVD Player, Blu Ray Disc and Multi Layer Blu Ray  Burners, Blue Ray DVD Players.

SS = single-sided, DS = double-sided, SL = single-layer, DL = dual-layer

Standard DVD Disc use a 650 nanometer Red Laser while the Blu-Ray Disk uses a 405 Nanometer Blue-Violet Laser.  A Nanometer is 1X10 to the -9 or one Billionth of a Meter.  The higher frequencies have smaller nm or Nanometer sizes and there can hold more data on the same size of disc.  Think of the colors of the Rainbow.  Red, Orange, Yellow, Green, Blue, Indigo, and Violet.  The lower frequencies are Red while the higher frequencies are Violet.  A good way to remember all of this is ROY-G-BIV and from this you can instantly remember the colors of the rainbow. 

  Here's some technical views on the Blu ray technology history.  It was always known that the blue light associated with the Blu Ray disc would provide a higher data density.  The blue light operates at such a higher frequency and therefore has a shorter wavelength.  The problem in development was that it was much more difficult to make a solid state laser in the blue frequency range and also difficult to make a disc medium that would accept the Blue Rays for writing and reading.  So as technology advanced you have seen it go from the older red laser light CDs and DVDs to the blue ray.  Next will probably be an ultraviolet ray, but, the solid state hard disk are now coming out with tremendous sizes of storage capability that the ultraviolet ray disk may never happen.  The camera memory is the leader in the solid state technology at a small package size and its size is growing tremendously. 

The next step in technology for the DVD Disc will be a solid state because it requires so much less energy, is technologically much more simple and it will have no moveable parts.  So pretty soon we will start seeing the video stores starting to package their DVD movies on solid state cards.  Hard disk and computer memory will also be merged into a single unit and the operation speed of the system will be greatly enhanced with less operations being required due to the removal of DOS, the Disc Operation System on the processors and less hardware in both computer chips and mechanical components.  Thing are changing really fast and there are changes coming really soon that we can't even imagine at this time.