Summary of How do CD-R discs work?
This article explains the mechanism of CD-R data storage. While standard CDs use physical bumps and flat areas to represent binary data, CD-R discs utilize a light-sensitive dye layer. A high-powered writing laser heats this dye to alter its transparency, creating permanent non-reflective spots that function as binary zeros. The text also notes that because the dye is sensitive to light, exposure to sunlight should be avoided to prevent damage before writing.
Parts used in the CD-R Disc:
- Plastic substrate
- Dye layer
- Reflective gold layer
- Laser (reading)
- Laser (writing)
If you have read the HowStuffWorks article How CDs Work, you know that the basic idea behind data storage on a normal CD is simple. The surface of the CD contains one long spiral track of data. Along the track, there are flat reflective areas and non-reflective bumps. A flat reflective area represents a binary 1, while a non-reflective bump represents a binary 0. The CD drive shines a laser at the surface of the CD and can detect the reflective areas and the bumps by the amount of laser light they reflect. The drive converts the reflections into 1s and 0s to read digital data from the disc. See How CDs Work for more information.
Normal CDs can not be modified — they are read-only devices. A CD-R disc needs to allow the drive to write data onto the disc. For a CD-R disk to work, there must be a way for a laser to create a non-reflective area on the disc. A CD-R disc therefore has an extra layer that the laser can modify. This extra layer is a greenish dye. In a normal CD, you have a plastic substrate covered with a reflective aluminum or gold layer. In a CD-R, you have a plastic substrate, a dye layer and a reflective gold layer. On a new CD-R disc, the entire surface of the disc is reflective — the laser can shine through the dye and reflect off the gold layer.
When you write data to a CD-R, the writing laser (which is much more powerful than the reading laser) heats up the dye layer and changes its transparency. The change in the dye creates the equivalent of a non-reflective bump. This is a permanent change, and both CD and CD-R drives can read the modified dye as a bump later on.
It turns out that the dye is fairly sensitive to light — it has to be in order for a laser to modify it quickly. Therefore, you want to avoid exposing CD-R discs to sunlight.
For more Detail: How do CD-R discs work?
- How does a CD drive read digital data?
The drive shines a laser at the surface and converts reflections from flat areas and bumps into 1s and 0s. - What represents a binary 1 on a CD?
A flat reflective area represents a binary 1. - What material is used for the extra layer in a CD-R disc?
An extra greenish dye layer is used to allow the laser to create non-reflective areas. - Can normal CDs be modified?
No, normal CDs are read-only devices and cannot be modified. - Why is the writing laser more powerful than the reading laser?
The writing laser must be more powerful to heat up the dye layer and change its transparency. - What happens when you write data to a CD-R?
The writing laser heats the dye layer, changing its transparency to create an equivalent of a non-reflective bump. - Is the change made by writing data to a CD-R permanent?
Yes, the change in the dye is permanent and can be read later by both CD and CD-R drives. - Why should you avoid exposing CD-R discs to sunlight?
The dye is fairly sensitive to light, so exposure should be avoided to prevent unwanted modification.
