The amount of time required to read a block of data from a disk into memory is Composed of seek time, rotational latency, and transfer time. Rotational latency refers to
a. The time it takes for the platter to make a full rotation
b. The time it takes for the read-write head to move into position over the appropriate track
c. The time it takes for the platter to rotate the correct sector under the head
d. None of the above
Rotational latency (sometimes called rotational delay or just latency) is the delay waiting for the rotation of the disk to bring the required disk sector under the read-write head. It depends on the rotational speed of a disk (or spindle motor), measured in revolutions per minute (RPM). For most magnetic media-based drives, the average rotational latency is typically based on the empirical relation that the average latency in milliseconds for such a drive is one-half the rotational period. Maximum rotational latency is the time it takes to do a full rotation excluding any spin-up time (as the relevant part of the disk may have just passed the head when the request arrived). Therefore the rotational latency and resulting access time can be improved (decreased) by increasing the rotational speed of the disks. This also has the benefit of improving (increasing) the throughput (discussed later in this article).