Compact disc
A compact disc, also called a CD is a storage device in the form of small plastic discs which store and retrieve computer data or music using light. Compact Discs replaced floppy disks because they were faster and could hold more information. The CDs made floppy disks become obsolete. CDs were invented by both Philips and Sony at the same time, but not together. Sony and Philips did work together to create a standard format and the technology to read CDs in 1982. CDs can hold up to 700 MB worth of data, which is about 80 minutes of music. Mini CDs were also made for special small programs like drivers. CDs that have computer information on them are called CD-ROMs, or Compact Disc - Read Only Memory. The diameter of a normal CD is 12 cm. The middle hole in a CD is about 1.5 cm.
Compact Disc Media
Diagram of CD layers- A polycarbonate disc layer has the data encoded by using bumps.*
- A shiny layer reflects the laser.*
- A layer of lacquer protects the shiny layer.*
- Artwork is screen printed on the top of the disc.*
- A laser beam is reflected off the CD to a sensor, which converts it into electronic data.*
Pits and Lands of a compact disc under a microscope
Comparison of various optical storage media
The pits in a CD are 500 nm wide, between 830 nm and 3,000 nm long and 150 nm deep.
Draufsicht auf Philips CDM 2/10 Laufwerk
Comparison of several forms of disk storage showing tracks (not to scale); green denotes start and red denotes end.* Some CD-R(W) and DVD-R(W)/DVD+R(W) recorders operate in ZCLV, CAA or CAV modes.
Sony CDP-101 from 1982, the first commercially released CD player for consumers
Philips CD100 from 1983, the first commercially released CD player in the US and Europe
Individual pits are visible on the micrometer scale.
700 MiB CD-R next to a mechanical pencil for scale
