Constant linear velocity
Encyclopedia
In optical storage
, constant linear velocity (CLV) is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs
. CLV implies that the angular velocity
(i.e. rpm
) varies during an operation, as contrasted with CAV
modes. The concept of constant linear velocity was patented in 1886 by phonograph pioneers Chichester Bell
and Charles Tainter.
An audio CD
employs constant linear velocity to maintain both a constant data rate and a constant bit density. At 1x speed the motor decreases from 495 to 212 rpm as the read head moves away from the center (which is the start of the recording), to keep the disc moving past the read head at a CLV of 1.2 m/s.
To accommodate the higher data transfer rates and random access requirements of modern CD-ROM drives, CAV
systems are used. This is because seek performance would be greatly affected during random access by the requirement to continually modulate the disc's rotation speed to be appropriate for the read head's position.
Zoned Constant Linear Velocity (ZCLV) is a modification of CLV for high speed CD and DVD recorder
s. Early model recorders were CLV drives. The recording speed on such drives was rated in multiples of 150 KiB/s; a 4X drive, for instance, would write steadily at around 600 KiB/s. The transfer rate was kept constant by having the spindle motor in the drive vary in speed and run about 2.5 times as fast when recording at the inner rim of the disc as on the outer rim. Some high-speed recorders use the zoned CLV method (ZCLV), which divides the disc into stepped zones, each of which has its own constant linear velocity. At higher speeds, ZCLV offers a compromise between CAV, which enables faster seek times, and CLV, which enables greater storage capacity. A ZCLV recorder rated at "52X", for example, would write at 20X on the innermost zone and then progressively step up to 52X at the outer rim.
format. The initial specification of CLV (as it applied to laserdisc) resulted in several playback artifacts to be present in the audio/video portion as well as compatibility problems with laserdisc players as produced by different manufacturers.
In the mid 1980s, Pioneer Electronics introduced the CAA scheme where the speed in rotation of the laserdisc was lowered in steps and eliminated most playback artifacts and compatibility problems. Since its introduction, most manufacturers of laserdiscs adopted the CAA format but still referred to their CAA-encoded product as CLV.
Optical storage
Optical storage is a term from engineering referring to the storage of data on an optically readable medium. Data is recorded by making marks in a pattern that can be read back with the aid of light, usually a beam of laser light precisely focused on a spinning disc. An older example, that does...
, constant linear velocity (CLV) is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...
. CLV implies that the angular velocity
Angular velocity
In physics, the angular velocity is a vector quantity which specifies the angular speed of an object and the axis about which the object is rotating. The SI unit of angular velocity is radians per second, although it may be measured in other units such as degrees per second, revolutions per...
(i.e. rpm
Revolutions per minute
Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
) varies during an operation, as contrasted with CAV
Constant angular velocity
In optical storage, constant angular velocity is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs...
modes. The concept of constant linear velocity was patented in 1886 by phonograph pioneers Chichester Bell
Chichester Bell
Chichester A. Bell was a chemist, cousin to Alexander Graham Bell, and instrumental in developing improved versions of the phonograph.- Life :...
and Charles Tainter.
An audio CD
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...
employs constant linear velocity to maintain both a constant data rate and a constant bit density. At 1x speed the motor decreases from 495 to 212 rpm as the read head moves away from the center (which is the start of the recording), to keep the disc moving past the read head at a CLV of 1.2 m/s.
To accommodate the higher data transfer rates and random access requirements of modern CD-ROM drives, CAV
Constant angular velocity
In optical storage, constant angular velocity is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs...
systems are used. This is because seek performance would be greatly affected during random access by the requirement to continually modulate the disc's rotation speed to be appropriate for the read head's position.
Zoned Constant Linear Velocity
DVD recorder
A DVD recorder , is an optical disc recorder that uses Optical disc recording technologies to digitally record analog signal or digital signals onto blank writable DVD media...
s. Early model recorders were CLV drives. The recording speed on such drives was rated in multiples of 150 KiB/s; a 4X drive, for instance, would write steadily at around 600 KiB/s. The transfer rate was kept constant by having the spindle motor in the drive vary in speed and run about 2.5 times as fast when recording at the inner rim of the disc as on the outer rim. Some high-speed recorders use the zoned CLV method (ZCLV), which divides the disc into stepped zones, each of which has its own constant linear velocity. At higher speeds, ZCLV offers a compromise between CAV, which enables faster seek times, and CLV, which enables greater storage capacity. A ZCLV recorder rated at "52X", for example, would write at 20X on the innermost zone and then progressively step up to 52X at the outer rim.
Constant Angular Acceleration
Constant Angular Acceleration (CAA) is a variant of CLV that was used on the LaserdiscLaserdisc
LaserDisc was a home video format and the first commercial optical disc storage medium. Initially licensed, sold, and marketed as MCA DiscoVision in North America in 1978, the technology was previously referred to interally as Optical Videodisc System, Reflective Optical Videodisc, Laser Optical...
format. The initial specification of CLV (as it applied to laserdisc) resulted in several playback artifacts to be present in the audio/video portion as well as compatibility problems with laserdisc players as produced by different manufacturers.
In the mid 1980s, Pioneer Electronics introduced the CAA scheme where the speed in rotation of the laserdisc was lowered in steps and eliminated most playback artifacts and compatibility problems. Since its introduction, most manufacturers of laserdiscs adopted the CAA format but still referred to their CAA-encoded product as CLV.