The Basics of CD-R Technology

While conventional CD players follow the Sony-Philips Red Book standard, CD-R conforms to the Orange Book part II standard. Once recorded, a CD-R disc meets the Red Book standard.

A recordable CD is the same size as a standard compact disc, but is more colourful. On top is a layer of gold (or silver); on the bottom is a recording layer made of blue cyanine dye. The Orange Book was written based on the original cyanine dye discs from Taiyo Yuden. Because of the gold layer behind it, the blue layer usually appears green.

Some CD-R discs use a yellow (gold like colour) dye of phthalocyanine. Claimed by the manufacturer, yellow dye lasts a little longer in accelerated aging tests, and it may work better with high speed CD-R drives. Still, most CD-R writers are optimized for cyanine dye, which can handle a wider range of laser power and wavelength. Cyanine dye is the de facto standard. Most CD-Recorders are optimized for cyanine dye.

There are CD-Rs available on the market that look entirely silver or gold. They are made with the diamond disc dye from Nissei Sangyo. The diamond disc dye is crystal clear. Once applied, the reflective layer of the CD-R simply appears the colour of the CD. Apart from being clear, the properties of the diamond disc dye are claimed to be almost identical to pthalocyanine dyes.

A blank CD-R is made of four layers:

  • A clear plastic layer (top) for the label. This layer also protects the gold or silver layer.
  • The gold or silver layer reflects laser light.
  • A layer of dye for the recording.
  • Another clear plastic layer (bottom) protects the dye layer.

The dye fills a spiral groove which is etched in the bottom clear-plastic layer. This groove guides the laser. To record data on disc, the laser melts holes in the dye layer. The plastic layer flows into the holes to form pits. During playback, the same laser reads the disc at lower power. At each pit, laser light reflects off the gold layer. The reflected light enters the laser reader, which detects the varying reflectance as the pits go by.

In contrast with a standard CD, a CD-R disc has two more data areas:

  • The Program Calibration Area (PCA). The CD recorder uses this area to make a test recording, which determines the right amount of laser power to burn the disc (4 to 8 milliwatts).
  • The Program Memory Area (PMA). This area stores a temporary table of contents (TOC) as the CD-R tracks are being assembled. The TOC is a list of the tracks, their start times, and the total program time. The recorder uses the Program Memory Area for this information until it writes the final TOC.
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