how removable storage works - clear polycarbonate
Optical storage the optical storage device that most of us are familiar with is a CD (CD).
CD can store a large amount of digital information (783 MB)
It is very cheap to make on a very small surface.
The design that makes this possible is a simple one: the CD surface is a mirror covered with billions of tiny bumps arranged in a long, tightly wound spiral.
The CD player reads the bump with a precise laser and interprets the information as a data bit.
The raised spiral on the CD starts at the center.
The CD track is too small to be measured in microns (
One in a million of 1 m).
The CD track is about 0.
5 micron wide with 1.
Separate 6 microns from one orbit to the next.
The elongated bumps are 0 each.
5 micron wide, the minimum is 0.
83 microns long, 125 nm (
One in ten million of 1 m)high.
Most of the quality of the CD is injected.
A piece of transparent polyester plastic molded, about 1.
In the manufacturing process, this plastic is impressed by the microscopic bumps that make up the long spiral track.
Then apply a thin reflective aluminum layer to the top of the disc, covering the raised.
The trickiest part of CD technology is reading all the tiny bumps correctly in the right order and at the right speed.
To do all this, the CD player must be very precise when it focuses the laser on the raised track.
When playing the CD, the laser beam passes through the polycarbonate layer of the CD, reflects the aluminum layer, and hits the photoelectric device that detects the change of light.
The light reflected by the bump is different from the flat part of the aluminum layer, which is called land.
The photoelectric sensor can detect these changes in the reflectivity, as well as the CD-
Player drive interprets the change as a data bit.