Compact Disc

Compact Disc
Name	Compact Disc
Caption	A standard 12 cm (4.7 in) read-only disc
Type	Optical disc
Encoding	Various
Capacity	Typically 700 MiB (up to 80 minutes audio)
Read	780 nm wavelength semiconductor laser
Standard	Rainbow Books
Developed by	Philips and Sony
Usage	Data storage, audio, video
Released	1982

Compact Disc. The Compact Disc is a digital optical disc data storage format that was co-developed by the electronics corporations Philips and Sony. It was first released to the public in 1982, revolutionizing the music industry by providing superior audio fidelity and durability compared to analog formats like the vinyl record and compact cassette. The format's success led to its adaptation for data storage of computer files, known as CD-ROM, and later for video as Video CD and Super Video CD.

History

The origins of the technology trace back to earlier optical recording inventions, including the work of James T. Russell at the Battelle Memorial Institute in the late 1960s. In 1979, Philips and Sony formed a joint task force to create a new digital audio disc standard, successfully merging Philips's early Laserdisc technology with Sony's error-correction methods. The companies announced the Red Book standard in 1980. The first commercial album released was Billy Joel's 52nd Street in Japan in October 1982, with Dire Straits' Brothers in Arms becoming one of the first major commercial successes. The format's adoption was accelerated by the support of major record labels and the introduction of the CD player by manufacturers like Sony, Philips, and Yamaha.

Physical characteristics

A standard disc is 120 mm in diameter, 1.2 mm thick, and has a 15 mm diameter center hole. It is constructed from a polycarbonate plastic substrate, a reflective metallic layer typically made of aluminium, and a protective lacquer coating. Data is stored as a series of microscopic indentations, or pits, and flat areas, called lands, arranged in a single, continuous spiral track from the inside to the outside of the disc. The track pitch is 1.6 µm. A thin layer of aluminium or, in later premium discs, gold or silver, provides reflectivity for the laser to read the data.

Data encoding and reading

Information is encoded digitally using a technique called Eight-to-Fourteen Modulation, which converts each 8-bit data byte into a 14-bit channel pattern for more reliable reading. This is further processed with a Cross-interleaved Reed–Solomon coding system for robust error correction. A low-power semiconductor laser with a wavelength of 780 nm (within the infrared spectrum) is focused through the disc's substrate onto the reflective layer. A photodiode detects changes in light intensity as the laser passes over pits and lands, converting these variations back into a digital electrical signal.

Audio format

The standard audio format, defined by the Red Book specifications, uses pulse-code modulation to digitize sound. Audio is sampled at a rate of 44.1 kHz with a bit depth of 16 bits per sample, providing a theoretical frequency response from 20 Hz to 20 kHz and a dynamic range exceeding 90 dB. This results in a data transfer rate of 176.4 kB/s for stereo playback. The format's introduction was heavily marketed with the slogan "Perfect Sound Forever" to emphasize its lack of hiss, wow, flutter, and wear associated with analog media.

Variants

Numerous derivatives were developed from the original audio format. The CD-ROM format, standardized in the Yellow Book, allowed for read-only computer data storage. CD-R and CD-RW, defined by the Orange Book, enabled users to record data once or multiple times, respectively. Other specialized formats include the Video CD (White Book), Photo CD, CD-i (Green Book), and enhanced audio discs like CD+G and CD-Text. The physical size also saw variations, most notably the smaller 80 mm Mini CD.

Manufacturing

Commercial replication is a high-volume, precision process of injection molding. A glass master disc is created using a laser beam recorder to etch data patterns into a photoresist layer. This master is then used to create a nickel stamper through electroforming. The stamper is mounted in an injection molding machine to produce clear polycarbonate substrate discs containing the pit-and-land structure. The discs are then metallized, spin-coated with a protective lacquer, and often screen-printed with artwork. The entire process is conducted in cleanroom environments to prevent contamination by dust.

Cultural impact

The format's arrival precipitated a massive industry shift, often called the "Digital Revolution" in music, leading to the decline of the vinyl record and cassette tape markets. It enabled new listening habits, such as random-access playback and the creation of personal compilations. The CD-ROM drive became a standard component in personal computers like the Apple Macintosh and IBM PC compatible systems, facilitating the distribution of encyclopedias, video games, and software. The format's success established the optical disc as the dominant digital distribution medium for decades, paving the way for the DVD and Blu-ray Disc.

Category:Optical disc authoring Category:Audio storage Category:Computer storage media Category:1982 introductions