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optical storage IBM defines optical storage as "any storage method that uses a laser to store and retrieve data from optical media." '' Britannica'' notes that it "uses low-power laser beams to record and retrieve digital (binary) data." Compact disc (CD) an ...
, 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 In physics, angular velocity or rotational velocity ( or ), also known as angular frequency vector,(UP1) is a pseudovector representation of how fast the angular position or orientation of an object changes with time (i.e. how quickly an objec ...
, contrasted with a
constant linear velocity 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 ...
(CLV). 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

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).''FUNDAMENTOS DE HARDWARE.'' – Page 37 of 45 (graphic)
/ref> 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

Gramophone record A phonograph record (also known as a gramophone record, especially in British English), or simply a record, is an analog sound storage medium in the form of a flat disc with an inscribed, modulated spiral groove. The groove usually starts near ...
s have always used CAV, including CEDs which provide video signals. Some high speed CD and DVD drives use CAV. It allows for shorter
access time Access time is the time delay or latency between a request to an electronic system, and the access being completed or the requested data returned * In a computer, it is the time interval between the instant at which an instruction control un ...
s 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 A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magn ...
. It also allows for the fastest writing speeds on recordable media (e.g.
CD-R CD-R (Compact disc-recordable) is a digital optical disc storage format. A CD-R disc is a compact disc that can be written once and read arbitrarily many times. CD-R discs (CD-Rs) are readable by most CD readers manufactured prior to the int ...
,
DVD±R DVD±R (also DVD+/-R, or "DVD plus/dash R") is not a separate DVD format, but rather is a shorthand term for a DVD drive that can accept both of the common recordable DVD formats (i.e. DVD-R and DVD+R). Likewise, DVD±RW (also written as DVD±R/W, ...
,
BD-R Blu-ray Disc Recordable (BD-R) refers to two direct to disc optical disc recording technologies that can be recorded on to a Blu-ray-based optical disc with an optical disc recorder. BD-R discs can be written to once, whereas Blu-ray Disc Recor ...
) 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 edition The terms special edition, limited edition, and variants such as deluxe edition, or collector's edition, are used as a marketing incentive for various kinds of products, originally published products related to the arts, such as books, prints, ...
s of certain films. 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 The Xbox is a home video game console and the first installment in the Xbox series of video game consoles manufactured by Microsoft. It was released as Microsoft's first foray into the gaming console market on November 15, 2001, in North Amer ...
discs, and Sega's
GD-ROM GD-ROM (an abbreviation of "Gigabyte Disc Read-Only Memory") is a proprietary optical disc format originally used for the Dreamcast video game console, as well as its arcade counterpart, the Sega NAOMI and select Triforce arcade board titles. It ...
.


Partial constant angular velocity (P-CAV)

If the used media (e.g.
DVD-RAM DVD-RAM (DVD Random Access Memory) is a DVD-based disc specification presented in 1996 by the DVD Forum, which specifies rewritable DVD-RAM media and the appropriate DVD writers. DVD-RAM media have been used in computers as well as camcorde ...
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. QPxTool glossary: P-CAV (partial constant angular velocity
/ref>


See also

*
Constant linear velocity 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 ...
(CLV) *
Zone bit recording In computer storage, zone bit recording (ZBR) is a method used by disk drives to optimise the tracks for increased data capacity. It does this by placing more sectors per zone on outer tracks than on inner tracks. This contrasts with other approa ...
(ZCAV) *


References

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External links

* http://www.pcguide.com/ref/hdd/geom/tracksZBR-c.html Rotating disc computer storage media Audio storage Video storage Optical computer storage