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Wow, I can't believe how BS this TDP is! I feel like a total idiot! I've always assumed it's sorta-kinda a tight upper bound on power consumption, perhaps with

Wow, I can't believe how BS this TDP is! I feel like a total idiot! I've always assumed it's sorta-kinda a tight upper bound on power consumption, perhaps with some allowance for "imperfections" in the dissipation properties of the CPU, and that I shouldn't sweat the details. Couldn't this count as false/misleading advertizing though?

vel0city 1y ago
Its pretty insane to see someone say something like: “TDP is about thermal watts, not electrical watts. These are not the same.” Watts are watts. But yeah, TDP means nothing. If you stick plenty of cooling and run the right motherboard board revision your "TDP" can be whatever you want it to be until the thing melts.
- o11c 1y ago
  "TDP is about average watts, not peak watts" would be an honest way of saying it.
  - vel0city 1y ago
    But in the end that's still not actually true in many modern desktop chips. You can take a 65W part, and with a "stock" motherboard firmware, good cooling, and the right workload end up averaging way more than 65W. Or if you have it in a hot room it just might end up using less than 65W. TDP is more of a rough idea of how much power the manufacturer wanted to classify the part as. It ultimately only loosely relates to the actual heat or electrical usage in practice.
gruez 1y ago
It's thermal design power, ie. it's the power that it's designed for, not absolute max.
- db48x 1y ago
  No, they don’t design the chip with these numbers in mind. The marketing department picks the number they want based on how they want customers to think about the chip, and which competitors they want you to compare it against. They just plug in whatever numbers are needed into the formula so that the number comes out how they want it.
  - gruez 1y ago
    >The marketing department picks the number they want based on how they want customers to think about the chip, and which competitors they want you to compare it against. They just plug in whatever numbers are needed into the formula so that the number comes out how they want it. Are you just describing product segmentation? ie. how the ryzen 5700x and 5800x are basically the same chip, down to the number of enabled cores, except for clocks and power limit ("TDP")?
    - db48x 1y ago
      Yep. The 5800X is a higher bin specifically because it can clock higher than the ones in the 5700X bin. That certainly makes them draw more power, so they give them a higher TDP number too. But the TDP doesn’t have anything to do with how much power the cpu will draw or how much heat it will generate in practice. Those numbers vary quite a lot; the CPU continuously adjusts it’s own frequency multiplier based on it’s own measured temperature, meaning it’ll draw more power if you cool it better.
      - gruez 1y ago
        >But the TDP doesn’t have anything to do with how much power the cpu will draw or how much heat it will generate in practice. Those numbers vary quite a lot; the CPU continuously adjusts it’s own frequency multiplier based on it’s own measured temperature, meaning it’ll draw more power if you cool it better. I don't get it, are you referring to the phenomenon that different workloads have different power consumption (eg. a bunch of AVX512 floating point operations vs a bunch of NOPs), therefore TDP is totally made up? I agree that there's a lot of factors that impact power usage, and CPUs aren't like a space heater where if you let it run at full blast it'll always consume the TDP specified, but that doesn't mean TDP numbers are made up. They still vaguely approximate power usage under some synthetic test conditions, or at the very least is vaguely correlated to some limit of the CPU (eg. PPT limit on AMD platforms).
- taneq 1y ago
  Huh, I always thought it was “total dissipated power”. Like you’d use to spec a power supply.
kllrnohj 1y ago
> Couldn't this count as false/misleading advertizing though? For what, exactly? TDP stands for "thermal design power" - nothing in that means peak power or most power. It stopped being meaningful when CPUs learned to vary clock speeds and turbo boost - what is the thermal design target at that point, exactly? Sustained power virus load?
- einpoklum 1y ago
  > For what, exactly? TDP stands for "thermal design power" The chip is not designed for this rate of power dissipation; and it is not the rate of power dissipation that you can expect to get from the chip.
  - kllrnohj 1y ago
    > The chip is not designed for this rate of power dissipation Says who? AMD advertises the chip as having a base clock of 4.3 GHz over all cores. The 9950X pulls somewhere around 220W at 5ghz all cores and with how power scales, 170W at the advertised 4.3 GHz seems more than plausible. Seems perfectly within reason that the advertised frequency and the advertised TDP are aligned. I wish Anandtech was still around as iirc they did have charts for all this, which nobody else seems to do :/ > and it is not the rate of power dissipation that you can expect to get from the chip. Again, says who? Who's expectations? This is a consumer chip, and the expectations of a consumer chip is not that it spends 100% of its time running prime95 or a similar "power virus" workload. I expect that if I buy this chip while I would have intervals of >170W, I'd also have long periods of much less than 170W. If I have a cooler designed to sustain 170W of cooling, that's going to work out on average just fine as there's thermal mass in the system.
    - einpoklum 1y ago
      > Says who? Says AMD and says Intel, apparently. At the link, there is an official explanation (sort of) how the TDP figure is derived.

vel0city 1y ago

Its pretty insane to see someone say something like: “TDP is about thermal watts, not electrical watts. These are not the same.” Watts are watts. But yeah, TDP means nothing. If you stick plenty of cooling and run the right motherboard board revision your "TDP" can be whatever you want it to be until the thing melts.

o11c 1y ago
"TDP is about average watts, not peak watts" would be an honest way of saying it.
- vel0city 1y ago
  But in the end that's still not actually true in many modern desktop chips. You can take a 65W part, and with a "stock" motherboard firmware, good cooling, and the right workload end up averaging way more than 65W. Or if you have it in a hot room it just might end up using less than 65W. TDP is more of a rough idea of how much power the manufacturer wanted to classify the part as. It ultimately only loosely relates to the actual heat or electrical usage in practice.

gruez 1y ago

It's thermal design power, ie. it's the power that it's designed for, not absolute max.

db48x 1y ago
No, they don’t design the chip with these numbers in mind. The marketing department picks the number they want based on how they want customers to think about the chip, and which competitors they want you to compare it against. They just plug in whatever numbers are needed into the formula so that the number comes out how they want it.
- gruez 1y ago
  >The marketing department picks the number they want based on how they want customers to think about the chip, and which competitors they want you to compare it against. They just plug in whatever numbers are needed into the formula so that the number comes out how they want it. Are you just describing product segmentation? ie. how the ryzen 5700x and 5800x are basically the same chip, down to the number of enabled cores, except for clocks and power limit ("TDP")?
  - db48x 1y ago
    Yep. The 5800X is a higher bin specifically because it can clock higher than the ones in the 5700X bin. That certainly makes them draw more power, so they give them a higher TDP number too. But the TDP doesn’t have anything to do with how much power the cpu will draw or how much heat it will generate in practice. Those numbers vary quite a lot; the CPU continuously adjusts it’s own frequency multiplier based on it’s own measured temperature, meaning it’ll draw more power if you cool it better.
    - gruez 1y ago
      >But the TDP doesn’t have anything to do with how much power the cpu will draw or how much heat it will generate in practice. Those numbers vary quite a lot; the CPU continuously adjusts it’s own frequency multiplier based on it’s own measured temperature, meaning it’ll draw more power if you cool it better. I don't get it, are you referring to the phenomenon that different workloads have different power consumption (eg. a bunch of AVX512 floating point operations vs a bunch of NOPs), therefore TDP is totally made up? I agree that there's a lot of factors that impact power usage, and CPUs aren't like a space heater where if you let it run at full blast it'll always consume the TDP specified, but that doesn't mean TDP numbers are made up. They still vaguely approximate power usage under some synthetic test conditions, or at the very least is vaguely correlated to some limit of the CPU (eg. PPT limit on AMD platforms).
taneq 1y ago
Huh, I always thought it was “total dissipated power”. Like you’d use to spec a power supply.

kllrnohj 1y ago

> Couldn't this count as false/misleading advertizing though? For what, exactly? TDP stands for "thermal design power" - nothing in that means peak power or most power. It stopped being meaningful when CPUs learned to vary clock speeds and turbo boost - what is the thermal design target at that point, exactly? Sustained power virus load?

einpoklum 1y ago
> For what, exactly? TDP stands for "thermal design power" The chip is not designed for this rate of power dissipation; and it is not the rate of power dissipation that you can expect to get from the chip.
- kllrnohj 1y ago
  > The chip is not designed for this rate of power dissipation Says who? AMD advertises the chip as having a base clock of 4.3 GHz over all cores. The 9950X pulls somewhere around 220W at 5ghz all cores and with how power scales, 170W at the advertised 4.3 GHz seems more than plausible. Seems perfectly within reason that the advertised frequency and the advertised TDP are aligned. I wish Anandtech was still around as iirc they did have charts for all this, which nobody else seems to do :/ > and it is not the rate of power dissipation that you can expect to get from the chip. Again, says who? Who's expectations? This is a consumer chip, and the expectations of a consumer chip is not that it spends 100% of its time running prime95 or a similar "power virus" workload. I expect that if I buy this chip while I would have intervals of >170W, I'd also have long periods of much less than 170W. If I have a cooler designed to sustain 170W of cooling, that's going to work out on average just fine as there's thermal mass in the system.
  - einpoklum 1y ago
    > Says who? Says AMD and says Intel, apparently. At the link, there is an official explanation (sort of) how the TDP figure is derived.