CDs, or compact discs, first emerged on the scene in the 1980s. They quickly became a phenomenon due to their seemingly magical ability to store high-quality audio on such a small and portable device. But how do CDs actually work? What’s going on under the shiny surface of a CD?
A CD is made up of several layers. The most important layer is the actual data layer. This layer is comprised of millions of tiny pits and bumps that hold the audio information. In order to read the data from the CD, a laser is used. The laser is directed at the surface of the disc, and as it moves across the data layer, it reads the bumps and pits by sensing differences in reflection.
When light hits a bump on the disc, it is reflected back in a different direction than it would be if it hit a pit. This change in direction is detected by a photodiode, which converts the reflected light into an electrical signal. The electrical signal is then processed by a computer and turned back into audio.
The laser that is used to read the data from a CD is incredibly precise. It is able to detect changes in reflection that are no more than a fraction of a wavelength of light. This makes it possible to read data that is encoded at a very high density on the surface of the disc.
The CD player uses a small motor to spin the disc at a constant speed. The data layer of the CD is arranged in a long, continuous spiral, starting at the center of the disc and moving outwards. The laser follows this spiral track, reading the data as it goes.
In addition to the data layer, a CD also has a layer of plastic on top and a layer of metal on the bottom. The plastic layer provides protection for the data layer, while the metal layer provides a mirror-like surface for the laser to reflect off of.
When a CD is manufactured, the data layer is imprinted onto a plastic disc using a stamping process. The data layer is then coated with a thin layer of metal, which provides the reflective surface. The plastic layer is added on top of the metal layer to protect the data from scratches and other damage.
CDs can store a tremendous amount of data, up to 700 megabytes. This is because the bumps and pits on the data layer can be arranged very densely. To put this in perspective, a typical 3-minute song takes up about 30 megabytes of space on a CD.
The data on a CD is also encoded using a process called interleaving. This means that the data is spread out across the surface of the disc in a way that makes it more resistant to errors caused by scratches or other damage. If one part of the disc becomes damaged, the CD player can use error correction techniques to rebuild the missing data using the surrounding information.
In addition to music CDs, there are also CDs that store other types of data, such as computer software or video games. These discs work in much the same way as music CDs, but they may use different types of encoding or be structured differently to accommodate the different types of data they store.
CD technology has come a long way since the 1980s. Today, there are many alternative formats for storing audio and other types of data, such as digital downloads or streaming services. However, CDs still have a strong following among audiophiles and collectors who appreciate the high-quality sound and physical packaging that come with a CD.
In summary, CDs work by using tiny bumps and pits on a plastic disc to hold audio information. A laser is used to read the data by sensing changes in reflection as it moves across the disc. CDs are incredibly precise, able to store up to 700 megabytes of information. They also use interleaving and error correction techniques to make the data more resistant to damage. While CDs may no longer be the dominant format for music and other types of data, they remain a beloved part of many people's collections.