compact disc (CD), Molded plastic disc containing digital data that is scanned by a laser beam for the reproduction of recorded sound or other information. After its commercial introduction in 1982, the audio CD became the dominant format for high-fidelity recorded music for several decades. The digital audio data encoded in a CD is converted to analog form to reproduce the original audio signal. Coinvented by Philips Electronics and Sony Corp. in 1980, the compact disc expanded beyond audio recordings into other storage-and-distribution uses, notably for computers (CD-ROM) and entertainment systems (videodisc and DVD). A traditional audio CD stored just over an hour of music. A typical CD-ROM contained up to 680 megabytes of data. Evolutions in disc and data-storage technology resulted in other types of optical-disc formats, such as DVDs and Blu-ray discs, all of which, as physical objects, looked largely identical to a traditional CD but were able to store vastly different amounts of data. During the first decade of the 21st century, technology that enabled high-bandwidth media streaming over the Internet began to be widely adopted, and CDs and similar physical media became increasingly obsolete by the 2020s.
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