From: charlesandmilly@gmail.com   
      
   > I was under the impression that they use the same laser to read CDs and DVDs   
   and a separate laser for the Blu.   
   >   
   > Maybe yours uses three..   
      
   Interestingly enough, with few exceptions, most devices use just two lasers   
   (one infrared and the other is ultraviolet), based   
   upon the wavelength and bandwidth involved of the frequency range to operate   
   the laser. DVD's actually have a high frequency   
   band in the infrared range than audio cd's do. Of course, Ultraviolet is   
   another much higher range altogether to operate the   
   Blu ray media.   
      
   The focus of the laser light depends upon what the media does and the media   
   used, especially with the infrared laser. Since   
   DVD's read non-contiguously (and non-sequentially), as they are not linear in   
   their reading of media, and yet CD's are very   
   linear and sequential, the laser treats these media (the CD and the DVD very   
   different). MP3's are even falling into this   
   category with "multi-format read" devices (however mp3's are much more   
   compressed audio than an audio CD).   
      
   With the help of the sled motor and the spindle motor.... The machine does its   
   thing.   
   Anyway, the laser spot has to read according to what the machine identifies as   
   a type of media in its tray within   
   the load/eject mechanism. Then the detector system and the comparator   
   determine correct focus. Based upon   
   the detection system's compensation, the wavelength it reads at, and the   
   frequency its reads to, it determines   
   whether it is a CD, a DVD, an mp3 or a blu ray disc. The output follows   
   through based upon what the machine   
   says it is. If not, you get an error. Either way, the machine answers you-   
   based upon what you put into it on the   
   basis of the standards for each media the machine performs on.   
      
   Hope this helps. Good Luck.   
      
   Sincerely,   
      
      
   Charles Lucas   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)