Compact Disc Digital Audio
Compact Disc Digital Audio (CDDA) is surely the most popular audio recording delivery media these days. The media itself is cheap, quality is very good, it's easy to use and it's playable virtually everywhere.
It was an instant success. It was introduced in the United States in 1983, and in the same year 30,000 players and 800,000 discs were sold. In 1986, the numbers raised to 3 million players and 53 million discs. In early nineties, players were selling at a rate of 9.2 million units each year, and at the same period of time an average of 288 million discs left store shelves.
Since the format was so amazingly successful, Sony and Philips got together again in 1987 to standardize Video CD (White Book). Later on, they would still cooperate in developing CD-ROM and CD-ROM XA (Yellow Book), Enhanced CD/CD Extra (Blue Book) and CD-R/CD-RW (Orange Book).
PCM audio is usually pressed on CD with the following characteristics:
There are also provisions in the standard for quadraphonic audio (4 channels, 22.05 kHz sampling rate), but it's very rarely used.
The data in a CD starts in the inside of the disc and is read in a spiral towards the outer edge. The standard defines that a CD can contain 74 minutes of audio (rumour has it that this number was decided so that Beethoven's 9th symphony would fit inside a CD). Later, manufacturers managed to push that limit to 80 minutes.
A CD is a disc of polycarbonate with a reflective layer. Pressed CDs have pits that are one quarter of the reading laser's wavelength deep so that the reflected laser beam either cancels or amplifies itself when overlayed with its echo, that way generating a binary method to store information. In the case of a CD-R, it contains a pigment that is burned by the writing laser so that the reading laser will deflect when hitting it. Parts not burned will let the laser pass through to the reflective layer.
A CD has a diameter of 12 centimeters / 4.7 inches. There's also a smaller physical format of only 8 centimeters.