What is the difference between constant linear and constant angular velocity? Why is one used in magnetic recording and the other in optical recording?

What will be an ideal response?

The speed of disks is measured in rpm, revolutions per minute. A revolution is 360 degrees, so when we say a hard disk rotates at 7,200 rpm we actually mean 7,200 × 360 = 2,592,000 degrees per minute. This is aconstant angular velocity because the disk rotates through the same angle in any given period.

If this is a disk (magnetic or optical) with a head over the track, the track will move under the head at a linear speed which we measure in cm/s or inches/s. The linear speed of the head is given by the distance round the track divided by the time for a revolution. Since the length of a track depends on where it is on a disk (smaller
near to the center) the linear speed of the head over the track is not constant; it increases towards the edge.