Glossary

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  C


Caddy
A plastic case in which the CD can be placed before being put into a reader or CD-Recorder.

Capacity
A CD usually has 650Mb organized into 335250 sectors of 2 kb each. This is equivalent to 74 minutes of high-quality sound. A CD can hold a minimum of 650 Mb but capacity depends on several factors such as rotation velocity or the pitch of the track. It is sometimes possible to record or copy more data that the nominal capacity (over writing) but some readers will have problems reading it.

CAV (Constant Linear Velocity)
This depends on the reading speed of the data track. Many magnetic storage media such as floppy-disks and hard-discs revolve at a constant angular velocity (a constant number of revolutions per minute) so the data on the outer edge is more widely distributed than in the center.

CD-DA (Compact Disc - Digital Audio)
Commonly known as a CD, this is an audio disc containing up to 74 minutes of high-fidelity stereo sound. Unlike a vinyl disc where the needle follows a groove with a variable depth and transmits vibrations, the laser beam detects the presence of hollows on the surface and transmits binary information (0 or 1). The sound is converted to a digital signal 44,1000 times a second, and its value is encoded into 16 bits (for example 1001 0101 1011 1101). Encoding one second of hi-fi sound takes 1.5 million bits. Other CD types exist: the CD-ROM, CD-ROM/XA, and the CD-I. Introduced in the US in 1983, CD sales overtook vinyl in 1986. The Red Book gives specifications for CD-DA.

CD-ROM (Compact Disc - Read Only Memory)
A CD format used to save computerized text, pictures or sound. CD-ROMs are similar to CD-DAs but use several tracks for data. A CD-DA reader cannot read a CD-ROM but a CD-ROM reader can read a CD-DA. A CD-ROM can hold the equivalent of 250.000 pages of text or 20.000 pictures at average resolution.

CD-ROM mode 1
Has three error detection and correction levels for computerized data.

CD-ROM mode 2
Has two error detection and correction levels for sound and videos.

CD-ROM/XA
(Compact Disc Read Only Memory eXtended Architecture)
A CD-ROM using mode 1 and mode 2 and enabling simultaneous reading of low-quality sound and data.

CD-Bridge Disc
A version of CD-ROM/XA readable by a CD-I or CD-ROM/XA reader.

CD-I (Compact Disc Interactive)
CD which can store data, sound, video, etc. The Green Book gives the specifications of the CD-I. It can only be read by one specific reader.

CDV (Compact Disc Video)
A version of the CD storing only video and sound.

CD-WO (Compact Disc – Write Once)
A CD writable only once (also known as a CD-R). A CD-WO complies with ISO standard 9660 and can be read by a CD-ROM reader.

CIRC (Cross Interleaved Reed-Solomon Code)
Error-correction method specially developed for use with CDs meeting Red Book standards.

Close Session
Closing a recordable CD session consists of writing the TOC onto the disc and preparing a lead-in area for the next operation.

Close Disc
Closing a CD prevents other write operations regardless of remaining free space. When the disc is closed, the lead-in area for the final session will not include the address for the next recording area.

CLV (Constant Linear Velocity)
Data speed in front of the pick-up head is constant. Disc rotation speed varies according to the position of the reading head.

CRC (Cyclic Redundancy Check)
Returns the number of blocks per second where CRC errors have been detected. This parameter varies between 0 and 75 blocks per second.

Cross Talk
See XT


  D


DAT (Digital Audio Tape)
System for recording onto special magnetic tape. Used for saving computerized information.

Data Area
An area of data beginning with reference number 00:00:00 (ISO 9660).

Data transfer rate
A CD-DA reader can transfer data at a rate of 150 kb per second. A CD-ROM 12x reader transfers at 1.8 Mb per second.

Digital audio
Each sample is coded using 16 bits.

Digital data
All computer data is digitalized.

Digitalize
To convert an analogue signal (a sound, a picture, etc.) to digital.

Disc Description Protocol
Protocol for describing CD sectors.

Disc at Once
Method for writing in a single session and by making only one pass. The TOC and the lead-in area are written in succession and must be compiled beforeh
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