5 ms·

TL;DR: Intel decided to "redefine" what TDP means to them so it aligns what they're doing and their marketing.

ajross 8y ago
TDP means what it always has. It's the maximal thermal power output of the processor. Input electrical power may fluctuate, but TDP was never an electrical parameter.
- craftyguy 8y ago
  Exactly. All of this confusion is from some expectation that "TDP = input power", which is totally incorrect.
- mtgx 8y ago
  In that case, reviewers and tech sites should either prioritize peak power or at least mention peak power numbers every single time TDP is mentioned, too, because peak power is at least as important as TDP. I know from past experience with laptops that tend to get hot, that if the laptop uses significantly more power than what you'd expect from the TDP, you will have a bad experience as a customer with that laptop. So at this point, TDP is definitely quite misleading to customers. Either scrap it completely or at least mention a more relevant metric to consumers.
  - 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 ago
      Input 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 ago
        In a CPU ~99% of it should be, how else is the power dissipated?
        snovv_crash 8y ago
        Where else would it be going to? The RGB LEDs?
        pooppaint 8y ago
        All 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?
  - deleted 8y ago
    [deleted]
- simion314 8y ago
  Shouldn't chip makers provide you a Max power usage number so you would know what power supply you need, if the CPU can draw double for an interval, then the GPU would do the same and your power supply does not enough extra power you maybe in trouble. The "scandal" was caused by the fact reviewers were getting different results and people would accuse people on not doing the benchmark right.
- makomk 8y ago
  On modern Intel processors, TDP isn't the maximum thermal output power of the processor. It's the thermal output power when it's throttling back its speed by a particular, arbitrarily-defined amount for thermal reasons. It's basically a marketing number. The electrical input power on the other hand is pretty close to the actual thermal output power and is roughly the number you should actually use when speccing out a cooling system for an Intel processor.
- tmd83 8y ago
  It's how much it's designed to dissipate right? Which depends on the cooling so by your meaning it's a vague number isn't it? I think from power/watt number on a cpu people expect two thing. How efficient it is for the performance (electric bill) where you need input power. How better a cooling I need will need the thermal power. But even with that the issue of Turbo makes it harder to quantify those two because it all depends on workload. If I recall correctly though even with all that if I understand correctly the peak power draw in intel gets throttled much easier than AMD whereas their TDP number (compared to AMD) artificially inflates their efficiency reputation. I do think they had been much more efficient than AMD specially pre Zen.
- magila 8y ago
  The difference between input power and thermal output of a CPU is negligible. A tiny amount of electricity is used for external signalling, the rest gets converted to heat. So in practice TDP can be treated as a limit on input power. In fact that's exactly what Intel CPUs do by setting PL1 equal to TDP by default.
  - ajross 8y ago
    Negligible over time. What has everyone inexplicably confused is that electrical draw is allowed to be higher instantaneously than the output cooling will allow to accommodate bursts of computation. And some how everyone thinks that's a bad thing. Again, TDP means the same thing now that it did 15 years ago.
    - toast0 8y ago
      What you've described is how it used to be, maybe you gets few seconds of usage over the TDP, but then the processor throttles back to hit the spec. That can still happen (and often does in laptops etc), but as described in the article, and many others, many to most motherboards sold as individual components are configuring the chips so that they will run at a higher power state for an indefinite time, so long as the temperatures stay within operating limits. It would be nice to know what the expected power input / heat output is in that state, so you can get cooling to match, and have it in turbo mode at all times when the CPU is being stressed. Cooling to the TDP only will (or should) get you the base clocks and a brief amount of turbo, but is likely to thermal throttle quickly. This also brings more into question the adequeacy or not of the thermal interface material used between the CPU die and the heatspreader -- if the CPU will run turbo for longer if you keep it cooler, there's more frustration about less heat efficient solutions.
deleted 8y ago
[deleted]

TDP means what it always has. It's the maximal thermal power output of the processor. Input electrical power may fluctuate, but TDP was never an electrical parameter.

craftyguy 8y ago
Exactly. All of this confusion is from some expectation that "TDP = input power", which is totally incorrect.
mtgx 8y ago
In that case, reviewers and tech sites should either prioritize peak power or at least mention peak power numbers every single time TDP is mentioned, too, because peak power is at least as important as TDP. I know from past experience with laptops that tend to get hot, that if the laptop uses significantly more power than what you'd expect from the TDP, you will have a bad experience as a customer with that laptop. So at this point, TDP is definitely quite misleading to customers. Either scrap it completely or at least mention a more relevant metric to consumers.
- 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 ago
    Input 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 ago
        In a CPU ~99% of it should be, how else is the power dissipated?
      - snovv_crash 8y ago
        Where else would it be going to? The RGB LEDs?
      - pooppaint 8y ago
        All 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?
- deleted 8y ago
  [deleted]
simion314 8y ago
Shouldn't chip makers provide you a Max power usage number so you would know what power supply you need, if the CPU can draw double for an interval, then the GPU would do the same and your power supply does not enough extra power you maybe in trouble. The "scandal" was caused by the fact reviewers were getting different results and people would accuse people on not doing the benchmark right.
makomk 8y ago
On modern Intel processors, TDP isn't the maximum thermal output power of the processor. It's the thermal output power when it's throttling back its speed by a particular, arbitrarily-defined amount for thermal reasons. It's basically a marketing number. The electrical input power on the other hand is pretty close to the actual thermal output power and is roughly the number you should actually use when speccing out a cooling system for an Intel processor.
tmd83 8y ago
It's how much it's designed to dissipate right? Which depends on the cooling so by your meaning it's a vague number isn't it? I think from power/watt number on a cpu people expect two thing. How efficient it is for the performance (electric bill) where you need input power. How better a cooling I need will need the thermal power. But even with that the issue of Turbo makes it harder to quantify those two because it all depends on workload. If I recall correctly though even with all that if I understand correctly the peak power draw in intel gets throttled much easier than AMD whereas their TDP number (compared to AMD) artificially inflates their efficiency reputation. I do think they had been much more efficient than AMD specially pre Zen.
magila 8y ago
The difference between input power and thermal output of a CPU is negligible. A tiny amount of electricity is used for external signalling, the rest gets converted to heat. So in practice TDP can be treated as a limit on input power. In fact that's exactly what Intel CPUs do by setting PL1 equal to TDP by default.
- ajross 8y ago
  Negligible over time. What has everyone inexplicably confused is that electrical draw is allowed to be higher instantaneously than the output cooling will allow to accommodate bursts of computation. And some how everyone thinks that's a bad thing. Again, TDP means the same thing now that it did 15 years ago.
  - toast0 8y ago
    What you've described is how it used to be, maybe you gets few seconds of usage over the TDP, but then the processor throttles back to hit the spec. That can still happen (and often does in laptops etc), but as described in the article, and many others, many to most motherboards sold as individual components are configuring the chips so that they will run at a higher power state for an indefinite time, so long as the temperatures stay within operating limits. It would be nice to know what the expected power input / heat output is in that state, so you can get cooling to match, and have it in turbo mode at all times when the CPU is being stressed. Cooling to the TDP only will (or should) get you the base clocks and a brief amount of turbo, but is likely to thermal throttle quickly. This also brings more into question the adequeacy or not of the thermal interface material used between the CPU die and the heatspreader -- if the CPU will run turbo for longer if you keep it cooler, there's more frustration about less heat efficient solutions.

deleted 8y ago

[deleted]