This article is missing information about P-CAV (partial constant angular velocity). Please expand the article to include this information. Further details may exist on the talk page.(July 2020)
In optical storage, constant angular velocity (CAV) is a qualifier for the rated speed of any disc containing information, and may also be applied to the writing speed of recordable discs. A drive or disc operating in CAV mode maintains a constant angular velocity, contrasted with a constant linear velocity (CLV).
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.
A typical CD-ROM drive operates in CLV mode, in contrast to a floppy or hard disk drive, or gramophone, which operates in CAV mode. In CAV mode, the spindle motor turns at a constant speed, which makes the medium pass by the read/write head faster when the head is positioned at the outside of the disk. In contrast, in CLV mode, the spindle motor speed varies so that the medium passes by the head at the same speed regardless of where on the disk the head is positioned.
If the disk is recorded at the same areal density throughout, then when read or written in CAV mode, the data rate is higher for the outer tracks than for the inner tracks, whereas in CLV mode, the data rate is the same everywhere.
An advantage of CAV mode over CLV is that the drive mechanism is easier to engineer (less expensive to build). Another advantage is that a device can switch from reading one part of a disk to reading another part more quickly, because in CLV mode, when the device moves the head in or out, it must change the speed of the disc.
Dimensions of a standard-size (12cm diameter) optical disc
In case of a 12 cm standard diameter disc, data at the outermost edge (6 cm from center) is accessed at 2.4 times the speed of data at the inner edge of the data-containing program area (2.5 cm from center).[1]
For a miniature disc with a diameter of 8 cm (radius of 4 cm), the speed ratio of outer to inner data edge is 1.6.
This means that, for example, if a disc is accessed at a constant angular velocity of ×24, the equivalent linear velocity is ×24 while accessed at the outermost edge of the data area while being ×10 at the innermost data area.
Uses
Constant Angular Velocity (CAV) LaserDisc, showing the NTSC field setup and individual scanlines.
Some high speed CD and DVD drives use CAV.[specify] It allows for shorter access times because the rotation speed (angular velocity) does not need to be changed when the laser seeks across the disc, similarly to the magnetic head of a hard disk drive. It also allows for the fastest writing speeds on recordable media (e.g. CD-R, DVD±R, BD-R) because the disc can spin at the highest physically possible angular speed throughout the entire writing process. A linear (data reading and writing) speeds of 2.4 times higher can be reached at the outer disc edge with the same angular (rotation) speed.
CAV was used in the LaserDisc format for interactive titles; it was also used with special editions of certain films.[2] CAV allowed for perfect still frames, as well as random access to any given frame on a disc. Playing time, however, was 30 minutes on each side (these discs are also known as "standard play"), as opposed to 60 minutes on each side for CLV-based discs ("extended play").
If the used media (e.g. DVD-RAM variants) has a linear (writing) speed limitation that can not be attained with physically supported angular (rotation) speeds at the inner edge of the recordable area, the disc writing can start off with a constant angular velocity, until the increasing linear velocity has reached the writing speed limitation of the disc.
At that point, the drive transitions into writing with a constant linear velocity.
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This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Constant angular velocity news newspapers books scholar JSTOR April 2012 Learn how and when to remove this template message This article is missing information about P CAV partial constant angular velocity Please expand the article to include this information Further details may exist on the talk page July 2020 In optical storage constant angular velocity CAV is a qualifier for the rated speed of any disc containing information and may also be applied to the writing speed of recordable discs A drive or disc operating in CAV mode maintains a constant angular velocity contrasted with a constant linear velocity CLV 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 A typical CD ROM drive operates in CLV mode in contrast to a floppy or hard disk drive or gramophone which operates in CAV mode In CAV mode the spindle motor turns at a constant speed which makes the medium pass by the read write head faster when the head is positioned at the outside of the disk In contrast in CLV mode the spindle motor speed varies so that the medium passes by the head at the same speed regardless of where on the disk the head is positioned If the disk is recorded at the same areal density throughout then when read or written in CAV mode the data rate is higher for the outer tracks than for the inner tracks whereas in CLV mode the data rate is the same everywhere An advantage of CAV mode over CLV is that the drive mechanism is easier to engineer less expensive to build Another advantage is that a device can switch from reading one part of a disk to reading another part more quickly because in CLV mode when the device moves the head in or out it must change the speed of the disc Contents 1 Dimensions 2 Uses 2 1 Partial constant angular velocity P CAV 3 See also 4 References 5 External linksDimensions Edit Dimensions of a standard size 12cm diameter optical disc In case of a 12 cm standard diameter disc data at the outermost edge 6 cm from center is accessed at 2 4 times the speed of data at the inner edge of the data containing program area 2 5 cm from center 1 For a miniature disc with a diameter of 8 cm radius of 4 cm the speed ratio of outer to inner data edge is 1 6 This means that for example if a disc is accessed at a constant angular velocity of 24 the equivalent linear velocity is 24 while accessed at the outermost edge of the data area while being 10 at the innermost data area Uses Edit Constant Angular Velocity CAV LaserDisc showing the NTSC field setup and individual scanlines Gramophone records have always used CAV including CEDs which provide video signals Some high speed CD and DVD drives use CAV specify It allows for shorter access times because the rotation speed angular velocity does not need to be changed when the laser seeks across the disc similarly to the magnetic head of a hard disk drive It also allows for the fastest writing speeds on recordable media e g CD R DVD R BD R because the disc can spin at the highest physically possible angular speed throughout the entire writing process A linear data reading and writing speeds of 2 4 times higher can be reached at the outer disc edge with the same angular rotation speed CAV was used in the LaserDisc format for interactive titles it was also used with special editions of certain films 2 CAV allowed for perfect still frames as well as random access to any given frame on a disc Playing time however was 30 minutes on each side these discs are also known as standard play as opposed to 60 minutes on each side for CLV based discs extended play CAV is used with the Nintendo GameCube Game disc and Wii Optical disc the original Xbox discs and Sega s GD ROM citation needed Partial constant angular velocity P CAV Edit If the used media e g DVD RAM variants has a linear writing speed limitation that can not be attained with physically supported angular rotation speeds at the inner edge of the recordable area the disc writing can start off with a constant angular velocity until the increasing linear velocity has reached the writing speed limitation of the disc At that point the drive transitions into writing with a constant linear velocity 3 4 See also EditConstant linear velocity CLV Zone bit recording ZCAV CD and DVD writing speed CD DVD and Blu ray writing speedsReferences Edit FUNDAMENTOS DE HARDWARE Page 37 of 45 graphic The Criterion Collection Ghostbusters voyagerco com Voyager Media Store Archived from the original on 1997 02 13 Retrieved 2012 04 30 QPxTool glossary P CAV partial constant angular velocity CDRLabs com Samsung SE 208GB Portable 8x DVD Writer Reviews CDRLabs 2014 12 03 Retrieved 9 August 2020 External links Edithttp www pcguide com ref hdd geom tracksZBR c html Retrieved from https en wikipedia org w index php title Constant angular velocity amp oldid 1082069903, wikipedia, wiki, book, books, library,
