Rotational speeds of drives

from Wikipedia, the free encyclopedia

When storing data on magnetic or optical disks, there are different principles for controlling the speed of rotation . A distinction is made between the following procedures:

CAV

CAV = c onstant a ngular v eLocity, ( English for, constant angular velocity ')

The plate rotates at a constant speed. The further the read head is moved outwards, the higher the relative speed between the head and the disk surface. Now there are two options:

  • The data rate remains constant, which means that the external density of the data is becoming ever lower and increasingly inefficient. The method is used for records , laser discs , GameCube drives and for the Xbox 360 drive in CAV mode. It was also used in hard disks that are to be regarded as historical today , as they had a constant number of sectors per track.
  • The density remains constant, which results in higher data rates on the outside. This method is used in modern hard drives with zone bit recording and also fast optical drives. The speed factors specified there (based on a speed prescribed for CD-Audio or DVD-Video, for example) are only achieved at the outer edge of the medium.

The advantage of the constant angular speed is that when accessing the inner and outer areas of the plate, no braking or acceleration is necessary, which reduces the time and energy requirements as well as wear.

CLV

CLV = c onstant l inear v eLocity, ( English for constant web speed ')

The further the reading head is moved outwards, the more the speed of the plate is reduced. The relative speed between the reading head and the surface remains almost constant, as does the data density and data rate. This technique is used with audio compact discs and traditionally with CD-ROM drives and was also used with laser discs.

CAA

CAA = c onstant a ngular a cceleration, ( English for constant angular acceleration ')

A variant of CLV that was used with the Laserdisc to solve technical problems with the CLV. The speed is continuously reduced the further the reading head is moved outwards.

PCAV

PCAV = p artial c onstant a ngular v eLocity, ( English for, in part, constant angular velocity "), combination of CAV and CLV

In the inner area of ​​the CD, the drive works with CAV technology; when a certain target linear speed is reached in the outer area, it then switches to CLV. Vibration sensors are sometimes also used and only when there is increased vibration is a switch to CLV in the inner area.

ZCLV

ZCLV = z one c onstant l inear v eLocity, ( English for, zone constant web speed), a plurality of CLV zones

The data carrier is divided into several (logical) areas ("zones"), each of which is read or written using CLV technology. For CDs, 16 × is a typical speed value for the first (innermost) zone, other zones are 20 ×, 24 ×, 32 ×, 40 ×, 48 ×. This method is used in particular with CD and DVD burners . During the burning process (based on the error rate) it can be checked whether the medium is suitable for the next speed level at all; if necessary, there is no need to jump to the next higher level in favor of write reliability.

Web links