CD R or Recordable CD Media 

CD-R or recordable CD media

A CD R or CD recordable is a write once format that can be used for digital scrapbooking storage or storage of any other type of digital information. The discs are purchased as blank CDR media and then information is recorded to them. The information, once recorded on this type of media, cannot be erased and when the disc capacity has been reached no other information can be recorded onto the disc.

These recordable media come in 650 MB (the initial standard) and 700 MB (the de-facto standard) capacities. The maximum rated speed for recording this media has been reached and is 52 times.

In order to achieve recording on CD media, a different technology and disc structure is required when compared to the read-only CDs such as audio CDs. A CD R consists of a clear polycarbonate base layer, which makes up most of the disc thickness. For read-only CDs, pits or indents which represent the digital code of the stored information are molded into the top of the polycarbonate. For CD-Recordable media, there are no molded pits. Instead, a spiral groove starting from the inner portion of the disc and ending at the outer portion is molded into the top of blank CDR media. The recording and reading laser light follow this spiral groove when the disc is being used.

The next layer that lies on top of the polycarbonate plastic base and spiral groove is a dye layer and this is where the digital information is stored. When blank recordable CDs are being recorded, the laser light alters the dye in very small spots inside of the spiral groove. These small spots represent the digital code of the stored information and are the equivalent of the pits or indents in read-only CD media.

CD R Cross Section

structure of a recordable CD or CD-R

 

For CD-Rs, there are three types of dyes that are used:

  • Phthalocyanine dye is light green in color and is the most commonly used dye. It is very resistant to light fading and degradation caused by elevated temperature and relative humidity. For long term storage, it is recommended that discs with the phthalocyanine dye are used.
  • Cyanine dye is a blue dye. This dye has shown to be less stable towards elevated levels of light, heat, and humidity.
  • Azo dye is generally deep blue in color and like the cyanine dye has shown much less stability than the phthalocyanine dye discs.

The next layer in a CD recordable is the metal reflective layer. When a recordable CD disc is being read, the laser light shines through the base of the disc (non-label side), hits a spot or non-spot area in the dye layer, and then hits the metal layer. The laser light then gets reflected back to create a signal that in turn constructs the digital code. The metal layer in CD recordable media can be silver, silver alloy, or gold. Gold is by far the most stable and for long term storage of digital scrapbooking projects or other files, CD-Rs using gold metal are recommended. In fact, the best combination for maximizing stability and longevity is a disc with a phthalocyanine dye and gold metal layer.

Depending on the dye and metal layer combination, recordable CDs appear different when looking at the base of the discs and this appearance can help determine the disc composition and its stability. For example:

  • phthalocyanine dye + gold metal layer: disc appears gold in color
  • phthalocyanine dye + silver metal layer: disc appears very light green color
  • cyanine dye + silver metal layer: disc appearance can be various shades of blue
  • cyanine dye + gold metal layer: disc appears green
  • azo dye + silver metal layer: disc appears deep blue in color and possibly other shades of blue

To finish the disc structure, a thin lacquer layer is added on top of the metal to protect it from chemical and physical damage and then a label or printable surface layer is the final layer in the recordable disc structure.

The recordable CD can be used for effective long-term storage of digital information if the right type of blank CDR media is chosen. The one negative is the low storage capacity compared to some other storage media available nowadays. This is usually only an issue when storing video or very high quality digital photos.

digital scrapbooking storage | compact disk | compact disc digital audio | cd read only memory | cd r

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