An audio compact disc, commonly referred to as a CD, is a digital storage medium used primarily for audio recordings. It is a round, flat disc made of polycarbonate with a diameter of 12 centimeters and a thickness of 1.2 millimeters. The disc is coated with a thin layer of aluminum to form a reflective surface.
Audio compact discs are encoded using the Pulse Code Modulation (PCM) technique, where the analog audio signal is sampled at a high frequency and converted into digital data. This digital data is then stored on the disc in a spiral track that starts from the center and extends towards the outer edge.
The audio data on the disc is read using a laser beam directed onto the surface of the disc. The beam reflects differently off the bumps and pits on the disc, which represent the binary 0s and 1s of the digital data. This reflected light is then converted back into the original audio signals using a photodiode sensor.
CDs became popular in the 1980s and quickly replaced analog audio formats like vinyl records and cassette tapes. They offer several advantages, such as superior audio quality, durability, portability, and the ability to quickly access and skip between tracks.
Besides audio, CDs can also store other types of data, such as software programs, videos, and documents. However, the term "audio compact disc" specifically refers to CDs designed primarily for audio recordings.
