Power Management
What is the break-even time used to decide whether powering off an idle block pays off?
- AThe years needed to recoup a chip's purchase price through electricity savings
- BThe idle duration needed for the energy saved by powering off to exceed the energy spent saving and restoring state and powering up
- CThe time from power-on until the chip fails
Show answer and explanation
Answer: B. The idle duration needed for the energy saved by powering off to exceed the energy spent saving and restoring state and powering up
Powering off reduces leakage, but saving and restoring state, recharging supply capacitance and restarting clocks cost fixed energy and time. For short idle periods, this overhead exceeds the energy saved, making it a net loss. OSes and power-management circuits predict idle durations and enter deep power-saving states only when the idle time is expected to exceed the break-even time.
- A. It is not about financial payback.
- B. Correct. If the idle period is shorter, it is better not to power off.
- C. It is not about lifetime.