3 ms·
That's for max frequency on a given process node. Power scales with voltage squared. But that doesn't say anything about wasted power. And dynamic scaling screw
by ethbro 9y ago
That's for max frequency on a given process node. Power scales with voltage squared. But that doesn't say anything about wasted power. And dynamic scaling screws that up in modern chips.
I believe I could summarize things by saying the only way you can really save energy* doing the same work+ is by using a different semiconductor process (either power/leakage-reduction-focused or smaller).
* For serious values of "energy"
+ Where the same work is not always true for a given task, if one optimizes an algorithm
- naikrovek 9y agoCan you explain the voltage squared thing? To me, power = voltage * current.
- etep 9y agoFor chips, power scales with voltage squared. Is also true that P=IV (since both are true, these observations cannot be in contradiction). Apparently, for chips, the current must be proportional to voltage also. Glossing over some details, turning on (off) a transistor is the same as charging (discharging) a capacitor. The energy stored on a capacitor is 1/2 C V^2. If you turn on and off the transistor periodically (say with frequency f) you use 1/2 C V^2 energy f times per second (energy per unit time is power). Normally the capacitance is ignored when discussing how power changes because for a given design the capacitance is a fixed quantity.
- Filligree 9y agoRunning a processor at higher frequency also requires increasing voltage, which increases effective capacitance by that same formula. That's not the primary cause of the power = frequency^2 rule, but actually adds a factor on top of that.
- mmwelt 9y agoEven for purely resistive loads, power is proportional to the square of the voltage: P = V * I But, I = V / R So, P = V * (V / R) = V^2 / R
- deleted 9y ago[deleted]