Compact Disk Drive

• The CDD installs in one of the external 5-1/4 inch drive bays in the front of the PC case. It is secured by machine screws. Some manufacturers offer special rail-like systems that mount on the CDD. These allow the drive to be removed from the PC without having to remove any screws.
  
  
• Data is stored optically on the surface of the disk. A laser attached to an arm that moves back and forth across near the disk surface and sends light toward the disk surface which is coated with of a thin layer of aluminum.
  
  
• Smooth areas called a lands reflect the light back to a photo diode located near the laser. The reflected light is read as a 1. Areas called pits are where the aluminum has been removed. When the laser light hits these, it is scattered and very little is picked up by the photo diode. The absence of light is read as a 0.
  
  
• CDD have become the predominant removable storage media for PCs and can store 700 Mbytes of data.
  
  
• A 4-pin cable from the power supply plugs into the CDD and provides power to it.
  
  
• Data to and from the motherboard is carried on a 40-pin IDE (Integrated Drive Electronics) cable.
  
  
• There are two types of Compact Disk drives available for PCs.
  
  
  1. CD-ROM (read only memory) is the older type. As the title implies it can only read CDs. It can read any standard CD and most CD-R type disks. It may be able to read some types of CD-RW disks too. A 24x CD-ROM unit costs about $30.
     
     
  2. CD-RW (ReWritable)units can read and write CD-R and CD-RW type disks. It can also read standard CD type disks.
     A 24x10x40 CD-RW unit costs about $115. The 24x10x40 means the unit can write at 24x, re-write at 10x and read at 40x, where x is 150Kbytes/sec.

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