self doubt

Question

Is this formula ALWAYS correct?

Average Disk Latency (in milliseconds) = 30000/RPM

Answer 1

Disk rotations per minute is given in the question which may differ from question to question.

Comments

so, what's the general formula for calculating Average Disk Latency?

---

Average time for disk access = Seek time + Rotational Delay + Time taken for data transfer.

From your question you can calculate rotational delay as:

3000 rotations in 1 min

1 rotation in 1/50 seconds= 20 milliseconds(Time taken for one rotation).

If not specified then, rotational delay can be taken as 1/2(rotational time).

Rotational Delay = 10 milliseconds.