Given that the time to read data off a 7200 rpm disk drive will be roughly 75% of a 5400 rpm disk, at what idle time of the 7200 rpm disk will the power consumption be equal, on average, for the two disks?

Given that the time to read data off a 7200 rpm disk drive will be roughly 75% of 5400 rpm disk, at 30% idle time of 7200 rpm disk will the power consumption be equal, on average for the two disk

Explanation:

Let the 7200-disk busy time = x (we need to calculate it)

As given in the question the in the given time to read data off a 7200 rpm disk drive will be roughly 75% of 5400 rpm disk. This mean that we equalize the equations of both disk power

7200-disk power = 5400-disk power

here we apply the formula to calculate the 7200 rpm disk busy time

4.0 * (1-x) + 7.9 * x = 2.9 * (1-x/0.75) + 7.0 * x/0.75

4.0 + 3.9 x = 2.9 - 3.87 x + 9.33 x

1.1 = 5.47 x - 3.9 x

we calculate the value for x

Hence x = 0.70

Applying formula to calculate the idle time.

Idle time = 1.0 - 0.70 = 0.30