How does a CD-R work?
To understand how CD-R technology works, let's examine
compact disc technology first. A standard CD-ROM is a disc with a thick layer of aluminum
sandwiched between layers of clear polycarbonate. The polycarbonate base has tiny
indentations stamped into it during molding. A reflective layer of aluminum is applied
onto the base and covered with another layer of polycarbonate, called a lacquer.
The CD-R drive writes onto a special compact
disc that has a gold layer instead of the familiar silvery aluminum layer inside audio
compact discs. However, the disc can be only written once. When information is recorded
onto the disc, a layer of organic dye is altered and can never be changed.
The surface of the reflective layer is called the land. The
tiny indentations are called pits. Like a phonograph record, a CD has information
physically recorded in plastic.
To read the disc, the CD player or drive focuses a laser
beam through the polycarbonate base onto the aluminum surface. As light from the beam
bounces off the reflective surface, the pits cause variations in the reflected light.
These variations are interpreted by the drive as binary "ones" and
Instead of having information embedded at the time of
manufacture, a recorddable compact disc is blank. There are other significant differences
that allow you to record on it.
First, the polycarbonate base of CD-R media does not have
any pits pressed into it. Instead, blank CD-R discs have a molded polycarbonate base with
a spiral pre-groove. The grooves act as a guide for the laser of the CD-R drive, allowing
it to write tracks very precisely on the disc.
Secondly, recordable compact discs do not have an aluminum
layer. CD-R media has a thick layer of organic dye on the polycarbonate base. The organic
dye is recording medium.
Thirdly, covering and protecting the dye is a very thin
layer of gold. Gold is used because it does not react to the dye and corrode, as do many
other types of metal. Gold is also highly reflective.
Special Thanks to Mr
Michael Tan of Convergent Systems
for the provision of the Yamaha CD-RW