What defines the time taken to position the sector on the platter under the read/write head?
A.
Rotational delay

B.
Seek time

C.
Response time

D.
Data transfer rate

Explanation:
Rotational Latency
To access data, the actuator arm moves the R/W head over the platter to a particular track while
the platter spins to position the requested sector under the R/W head. The time taken by the
platter to rotate and position the data under the R/W head is called rotational latency. This latency
depends on the rotation speed of the spindle and is measured in milliseconds. The average
rotational latency is one-half of the time taken for a full rotation. Similar to the seek time, rotational
latency has more impact on the reading/writing of random sectors on the disk than on the same
operations on adjacent sectors.
Average rotational latency is approximately 5.5 ms for a 5,400-rpm drive, and around 2.0 ms for a
15,000-rpm (or 250-rps revolution per second) drive as shown here. Av. rotational latency for 15K
rpm or 250 rps (15000/60) drive is = (1/2)/250=2 milliseconds.
EMC E10-001 Student Resource Guide. Module 2: Data Center Environment