A compact disc, also known as a CD, is a plastic optical disc with a metalized surface that is used for digital audio storage.
When a compact disc is played, the information is read by a laser and converted into sound that represents an original audio source. The CD's storage capabilities have expanded alongside its technology to read other data like CD-ROM for computers or DVD and Blu-ray for video.
A standard CD typically holds 74 to 79 minutes of audio. The CD debuted in 1982 under Philips Electronics and Sony Corporation. The basic compact disc is simple in appearance, but consists of multiple layers. The base layer is polycarbonate plastic which holds the digital data.
This layer is topped by an aluminum coating that serves to reflect the laser that reads the disc's information. (In rare instances, silver or gold may be used in place of aluminum). A clear layer of shiny acrylic protects the aluminum. The standard CD has a 12 cm diameter and a 1.2 mm thickness. From its center outward, it consists of a spindle, a clamping ring, a stack ring, a mirror band, an information area and the rim.
The CD's data layer is comprised of billions of tiny indentations called pits that are invisible to the human eye. These pits are encoded with binary data (0's and 1's) that maintain the disc's speed and sound. They also serve to control the disc player's laser. The patterns of pits rest along tightly coiled spiral tracks followed by a laser. The reflected laser beam hits a photodiode that converts the binary data into an electrical signal that is heard like the original audio.
To achieve the sound of the original audio, the disc's binary data goes through a digital-to-analog converter at a 16-bit rate. From there, a low-pass filter restructures the original wave form to attain the sound that is heard. Use the links below to learn about each of the different types of recordable CDs.
- CD-ROM - A data disc format designed for Read-Only use in computer storage applications.
- CD-R - The write-once recordable CD explained in detail.
- CD-RW - Information about ReWriteable CDs and how they work.
- Printable CDs - Learn more about Printable CDs on this page.