Step-by-step Solution:

To calculate the average latency time of a hard disk with a rotational speed of 6000 RPM (rotations per minute), we use the formula: \[ \text{Average Latency Time} = \frac{\text{Time for One Full Rotation}}{2} \] Step-by-Step Solution:
1. Rotational speed = 6000 RPM
Convert RPM to rotations per second: \[ 6000 \, \text{RPM} = \frac{6000}{60} \, \text{rotations/second} = 100 \, \text{rotations/second} \]

2. Time for one full rotation:
\[ \text{Time for one rotation} = \frac{1}{\text{rotations/second}} = \frac{1}{100} = 0.01 \, \text{seconds (10 ms)} \]

3. Average latency time is half the time for one full rotation: \[ \text{Average Latency Time} = \frac{0.01}{2} = 0.005 \, \text{seconds} = 5 \times 10^{-3} \, \text{seconds} \]

Correct Answer: A. 5 × 10⁻³ sec