What is the average rotational latency of a disk drive that

What is the average rotational latency of a disk drive that rotates at 7200 RPM?

Solution

Disk rotates at 7200RPM
Average Rotational Latency = Maximum Rotational Latency / 2
Maximum Rotational Latency = How much time a point on a disk take to reach the same location after complete rotation
                       = 1 / (7200 rotations per minute)
                       = 1 / (7200 rotations per 60 seconds)
                       = 60 / 7200
                       = 8.3ms
Average Rotational Latency = 8.3/2
                       = 4.2 ms