Andrew S. Tanenbaum (OS) Edition 4 Exercise 5 Question 18 (Page No. 431)

Question

A disk rotates at $7200$ RPM. It has $500$ sectors of $512$ bytes around the outer cylinder. How long does it take to read a sector?

Answer 1

$7200\;\text{RPM} = 60 \; \text{seconds} \\ \Rightarrow 1 \; \text{sec} = 120 \; \text{RPM}$

$\therefore 1$ rotation $= 8.33\;\text{msec}$

To get sector time, we need to divide one rotation time by $500$

$\therefore $ Sector time $ = \frac{8.33}{500} = 16.67 \mu \text{sec}$