* Polycarbonate plastic

                         * Aluminum

                         * Acrylic

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            What are these materials?:                                          

                             Aluminum- a silvery ductile metallic element found primarily in bauxite       Source

                                      Formula: Al

                                      Atomic Number: 13

                                      Molecular Weight: 26.98

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            Structures of the materials:

The polycarbonate chain        Source                                The Aluminum Structure        Source   Acrylate Methacrylate                            The acrylic Structures            Source

          All about the spiral:                                                                                                                                             

                  * Every CD has its' own spiral, which can be located on the back side of the CD.                                               

                  *The spiral starts closest to the center (where the hole is) and works its' way towards the outside.

                  *Because of where the spiral starts,  the CD is made to be smaller then 4.8 inches or 12cm. 

                  *This spiral creates something known as the data track. 

                  *This track is were all the information is stored on a CD.  

                  *The data track is roughly 0.5 microns wide, and there are 1.6 microns separating one track from the next.  

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            All about the bumps:       

                   *0.5 microns wide

                  * minimum of 0.83 microns long

                  *125 nanometers high  

                  *These bumps can be found below the polycarbonate layer

                  *Can also be called pits.                                                                                                                                   

                  *If you took the data track off a CD and stretched it out it would measure 0.5 microns wide and almost 3.5 miles long!                          

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         * The laser tracks a CD by its' bumps so it can read the data (which is located on the data spiral)                                    

           * In order for the laser to move between songs( switch songs), this means that the data must be encoded into the music/ or data to let the drive know where it can be found on the CD.

         * Lasers sometimes misread a bump when reading a CD, and that is why there is something called error-correcting codes.  In order for this not to happen we try to avoid it by placing extra data bits (this tells the drive to detect these errors and also tells the drive how to correct it).

           *  Things are able to damage the CD and when this happens, the laser might not be able to read the whole CD. 

           * When a CD is misread it's known as a burst error

           * This is solved by interleaving.

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