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.
- 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.
- 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.