CAV
Constant Angular Velocity. A method for accessing data on optical discs. The disc rotates at a constant speed no matter where on the disc surface the data is located. This is a simpler and cheaper method to implement than CLV, because the drive motor speed does not have to change. (See also PCAV, CLV and ZCLV)

CD
Abbreviation for Compact Disc.

CD-DA
Compact Disc Digital Audio, defined in the Red Book.

CD-EXTRA
Alternative name for Enhanced Music CDs. A multisession compact disc that contains both audio and data tracks. The audio tracks can be accessed by CD players, and data tracks (typically containing multimedia content) can be accessed by a CD-ROM player in a computer. The CD-EXTRA specification is defined in the Blue Book.

CD-i
Compact Disc interactive (CD-i), a proprietary CD-ROM format developed by Philips that allows interactive multimedia applications to be run on a special player attached to a TV. The CD-i specification is defined in the Green Book.

CD-i Bridge
A CD-ROM XA disc with a CD-i application program able to be played on CD-i players.

CD-R
Compact Disc Recordable. CD-Rs allow data to be written either once only or in sessions for a multisession disc. This allows the data to be updated and/or added to until the disc is full. The data on a CD-R disc cannot be erased or re-written, hence their alternative name WORM (Write Once Read Many) disc. The CD-R specification is defined in the Orange Book.

CD-ROM
Compact Disc Read Only Memory. A compact disc used for storing computer data and for multimedia and games applications. The CD-ROM specification is defined in the Yellow Book.

CD-ROM XA (CD-XA)
Compact Disc Read Only Memory Extended Architecture, an extended version of the CD-ROM disc. CD-I, Video CD, Photo CD and CD EXTRA discs are based on the CD-ROM XA specification. The CD-ROM XA specification is contained in an extension to the Yellow Book.

CD-RW
CD-ReWritable disc. Using phase-change technology, they can be written to, erased and re-written a large number of times.

CD-TEXT
An superset of the CD-DA audio CD format that allows up to 5,000 characters of text information such as the artist, album name, and song names to be stored along with the song files. A CD player that recognises this information can read and display it for you.

CD-XA
See CD-ROM XA.

CLV
Constant Linear Velocity. A system used on older CD drives which alters the rotational speed of the disc depending upon where the data is located. The aim is to maintain a constant data transfer rate, and since less data can fit on the inside tracks of the disc than the outside, it has to rotate faster closer to the disc centre.
(See also CAV, PCAV and ZCLV)

CMYK
(C)yan-(M)agenta-(Y)ellow-(K)ey (which is black). A colour model for colour printing. Artwork submitted ready for printing on discs or paper parts must use the CMYK colour model (NOT RGB!), otherwise unknown results will occur. (See also RGB)

Codec
Coder/decoder. A device or software that encodes and decodes digital information, eg. video codecs allow different video formats to be played, manipulated and compressed.

Colour Disc/DVD
A standard CD or DVD, except the polycarbonate base of the disc is coloured, not clear, giving a very special appearance. They are available in a variety of different colours.

Compression
The conversion of data to a more compact form for storage or transmission. Compression can be lossy (used where there is redundant information in the original data) or lossless (where the original data can be recovered in its entirety).

Copy Protection
A technique used on CD and DVD discs to prevent the contents being copied and/or re-used. Technologies used include watermarking, signatures on disc and encryption.

CRC
Cyclic Redundancy Check used to check whether a data stream has suffered any corruption producing errors