A typical CD will have a diameter of just 12 cm and about 80 minutes audio data can be stored on it. Smaller CDs are also manufactured for storing just one songs (called CD singles). They are 8 cm in diameter and can save 24 minutes of audio data.



The key research and enhancement work was done by Phillips and Sony. One of the first CDs came in bazaar way back in the year 1982 and till date, remains one of the most widespread mode of audio recordings.

In 1979, Phillips and Sony launched off a joint working group in order to devise a successful digital audio disc. After a year`s work and lot of testing and planning, the compact disc was invented. No solitary person can be said to have invented it, a large group collectively invented the compact disc.

In August, 1982, the earliest CD for business intention was manufactured in a Phillips factory in Germany. The first music track that was released on a CD was `The Visitors (1981) by ABBA`. Shortly after, in October of the same year, the CD players from Sony also reached the markets. The event is often called as `the Big Bang` in the field of digital audio.

The new model was an immediate success in the bazaar. Consumers were excited about the quality of the audio on the CDs. The value of CD players sank really fast, as a result of which, the popularity increased even more.

A Compact Disc is a 1.2 mm thick polycarbonate plastic disc weighing around 16 grams. To make the surface reflective, a very thin layer of aluminum is spread on one side of the disc. A film of lacquer is also spread to act as a protecting shield. The label is printed on the other side using normal printing process like offset or screen printing. The data is stored on a CD in form of an array of tiny grooves called pits that are arranged in a spiral track. A pit is just 500 nm wide and 100 nm deep and the length varies from 850 to 3500 nm.

The CDs are much more durable than the previous formats of audio storage. However, they can be damaged a little from the environment factors and daily usage. The data is a lot closer to the label side, so more damage occurs if scratches are made of the label. The logical format to store audio data on a CD is a 2-channel 16-bit PCM encoded data at a sampling rate frequency of 44.1 KHz. The sampling rate was chosen directly as a result of the sampling rate theorem of double frequency needed in recordings. With some more calculations, the exact sampling rate of 44.1 KHz was decided.