The Free On-line Dictionary of Computing (30 December 2018):

constant angular velocity

    (CAV) One of the two schemes for controlling the rate of
   rotation of the disk in a disk drive.  Constant angular
   velocity keeps the rate of rotation constant.  This means that
   the linear velocity of the disk under the head is larger when
   reading or writing the outer tracks.  This in turn implies
   either a variation in the data rate to and from the heads or the
   bits per unit length along the track.

   The alternative, constant linear velocity, requires the rate of
   rotation of the disk to accelerate and decelerate according to the
   radial postion of the heads, increasing the energy use and
   vibration.

   (2014-07-16)