Compact Disc
History
The CD, short for Compact Disc, was first developed in the early 1980s by Philips and Sony. The two companies collaborated to create a standard format and player that would be universally accepted. The first publicly available CD player, the Sony CDP-101, was released in Japan on October 1, 1982.
The development of the CD was influenced by the success of the LaserDisc format, which was introduced in 1978. The LaserDisc was the first optical disc storage medium, and it demonstrated the potential of using a laser to read data from a disc. The CD improved upon the LaserDisc by being smaller, having a greater storage capacity, and being able to store digital data.
Design
A CD is a plastic disc with a reflective metal layer that stores digital data. The data is stored as a series of tiny indentations, known as "pits", on the metal layer. The pits are arranged in a spiral track that starts at the center of the disc and ends near the edge. A laser in the CD player reads the pits by reflecting light off the metal layer.
The CD is 120 millimeters in diameter and 1.2 millimeters thick. It is designed to hold up to 74 minutes of uncompressed audio or 650-700 megabytes of data. However, the capacity can be increased by using different methods of data compression.
Data Encoding and Reading
The data on a CD is encoded using a method called EFM. This method converts eight bits of data into fourteen bits, which reduces the chance of errors when the data is read. The fourteen bits are then encoded as a series of pits and "lands" (the flat areas between pits) on the CD.
A CD player reads the data by shining a laser onto the disc. The laser light is reflected back to a sensor, which detects changes in the intensity of the light. The sensor interprets the changes in light intensity as a series of ones and zeros, which are then converted back into the original data.
CD Formats
There are several different formats of CDs, each designed for a specific type of data:
- CD-DA: This is the standard audio CD format. It is used to store music and other audio content.
- CD-ROM: This format is used to store computer data. It can hold software, games, and other types of data.
- CD-R and CD-RW: These formats can be written to by a computer. CD-R discs can be written to once, while CD-RW discs can be erased and rewritten.
- Video CD: This format is used to store video content. It was popular in Asia in the 1990s, but has largely been replaced by the DVD.
Impact and Legacy
The CD had a significant impact on the music industry and on consumer technology. It was the first digital format for music, and it offered a significant improvement in audio quality over previous analog formats, such as the vinyl record and the cassette tape. The CD also paved the way for other digital media formats, such as the DVD and the Blu-ray disc.
Despite the rise of digital downloads and streaming services, the CD remains a popular format for music. As of 2020, billions of CDs have been sold worldwide, and many artists continue to release their music on CD.