8 ms·
> that if the laptop uses significantly more power than what you'd expect from the TDP You're falling into the "TDP is power input" trap.. TDP and power input
by craftyguy 8y ago
> that if the laptop uses significantly more power than what you'd expect from the TDP
You're falling into the "TDP is power input" trap.. TDP and power input are not the same. You can have a chip that takes less power to operate at a TDP equivalent to another chip which takes more power to operate.
Edit: There is no way that 100% of output power in a CPU is thermal, else it would be nothing but a very expensive heater. Also, CPUs do not operate in a closed environment, like those replying to me here seem to think.
- mindslight 8y agoInput power equals output power is a fundamental physical rule, not a "trap". Yes, average (thermal) output power does not equal instantaneous (electrical) input power (ie thermal mass), but it averages out. What the article is pointing out that TDP is thermal design power. Meaning a nameplate value that was targeted for "standard" operation, even though the processor can do higher. So if something has a TDP of 100W, yet the heatsink can maintain proper operating temperature while dissipating 150W, then the processor might sit there drawing (and dissipating) 150W the whole time. As an aside, I really wish CPU cooler manufacturer/reviews would start simply stating the thermal resistance - basically the single number that characterizes its effectiveness. I know it would undermine the dog and pony show of building a test system with so-and-so's motherboard etc running benchmarks, but the entire goal of science is to weed out the extraneous narrative.
- craftyguy 8y ago> Input power equals output power is a fundamental physical rule, not a "trap" No shit. The trap is thinking that all output power is thermal (it's not).
- p1necone 8y agoIn a CPU ~99% of it should be, how else is the power dissipated?
- snovv_crash 8y agoWhere else would it be going to? The RGB LEDs?
- pooppaint 8y agoAll output power is thermal though. This is basic thermodynamics. A negligible amount of input power will be distributed outside of the CPU die which will be dissipated as heat a short distance away. Pray tell, what other energy form do you think this input is becoming anyway?
- BeeOnRope 8y agoWell some power is used to run the fans which ends up partly turning into kinetic energy of air leaving the case. Sure, that may also manifest itself as heat somewhere down the line, but not in a way that is relevant for this discussion (and indeed you have to draw the line somewhere). It's probably fairly neglible though, probables less than a watt in most systems.
- jackvalentine 8y agoThe fans aren't the CPU.
- BeeOnRope 8y agoOops, you are right.
- p1necone 8y agoI imagine some tiny percentage would instead be dissipated as light/radio waves or sound too - hence my ~99% comment. There's also this: (https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle) if you want some light reading.
- pooppaint 8y agoIndeed there will be some piezoelectric effect and some EM emissions on the order of micro watts compared to the 10s of watts burned by the CPU. But the poster I was replying to seemed quite confused about the fate of power in a CPU used for computation: It’s dissipated as heat.
- effie 8y agoCPUs do no thermodynamic work. They do computational work, which does not count as work in work-heat-energy balance. All electrical energy consumed by CPU turns into increased internal energy of the surroundings, which is, in short, called heat.
- craftyguy 8y agoNot all of the electrical energy consumed by the CPU is used by the CPU for computational work. Some of the electrical energy transfers out of the CPU to other components. The TDP of the CPU is not concerned with those other components. TDP is not a useful measurement of the amount of electrical energy a CPU can consume.
- effie 8y agoAll consumed energy is used to produce heat, by definition of "consumption". If some electrical energy transfers out of CPU to other components (this is indeed possible), then by definition this energy is not consumed by the CPU. The meaning of TDP is explained in the article - Intel's value of TDP was such a measure, but is no longer so.