CS 2734
Computer Organization II
CD Rom Drives
- To write a CD:Information is recorded on a CD ROM by burning holes (pits) in the disk.
The unburned areas are called the lands. The process uses etching
to produce a master.
- To read a CD:
- A small laser diode (about 850 nm wavelength)
is shown through a beam splitter and relected off the
movable mirror.
- When beam strikes a land it gets reflected back through the mirror
and the beam splitter.
- When it hits a land, it is reflected all over.
- The beam gets reflected back off the mirror and into a photodetector
which produces a bit pattern.
- Recording information:
- Data is recording in a spiral.
- CD does not spin at constant rate, but rather traverses its spiral
at a constant rate.
- Most CD ROMS now use a SCSI interface. (This will be a future D'vice.)
- Other types of CD's:
- CD-R: special CD's are coated with a special film. The laser burns the coating.
This is slow.
- WORM (write once read many): has a second, more intense laser called a write
laser which is intense. It burns through a coating.
- Magneto-optical drives: use polarization by magnetic fields on electromagnetic
waves (read and write).
- Other links of interest:
Revision Date: 1/29/98