Yamaha 6416 CD-RW - Part 2

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/green/blue layer instead of the familiar silvery aluminum layer inside audio compact discs. This layer is typically made up of photosensitive organic dye. However, the disc can only be written once. When information is recorded onto the disc, a layer of organic dye is altered, irreversibly changing it's optical characteristics. Due to it's high reflectance, the CD-R disc is still playable on normal CD players.

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 "zeros."

Instead of having information embedded at the time of manufacture, a recordable compact disc is blank. There are other significant differences that allow you to record on it.

When information is recorded onto the disc, a layer of organic dye is altered, irreversibly changing it's optical characteristics. 

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 usually 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.

< Previous  

Next >