AMD rates it as non-turbo usage, ex: my $200 3600 is 65W TDP, has a package limit of 88W, and is designed to reach 65W without turboing; if I manually set the package limit to 65W, all cores will sit at the base clock of 3.6GHz forever. 88W hard package limit will be enforced under overclocking unless overridden by user.
The comparison is the $250 9600k, same single-threaded performance, 3600 is roughly 30% faster in multi-threaded; 95W TDP, soft package limit of 150W, and will exceed that under some situations under stock, and will absolutely exceed it overclocked.
So, Intel, in this case, costs 25% more, has 30% less performance, has 46% more TDP, and 70% more actual maximum usage... and to add insult to injury, AMD's stock cooler is beefier than Intel's: I believe AMD's stock cooler can sink 88W, I do not believe the Intel one can manage 150W+.
As you said, Intel's stock coolers are known for being loud, aren't actually too great at dissipating heat, and aren't even included on higher TDP chips. So you're almost automatically spending an extra $20+ over the chip price on a decent cooler.
On the other hand, AMD ships solid coolers with (pretty much?) every chip. I've run my R5 1600 with the stock cooler for two ish years without any real heat or noise issues.
In the case of Intel, the claimed TDP is a fairy tale.
So as you said, its "just a slightly worse binned version" but worse in terms of max clock not performance/watt.
Although there isnt a 'hard' definition of TDP AMD has typically rated there chips more accurately[ii] than intel in the past , but that said AMD's TDP is still lower than absolute max power draw.
[i]- Memories from working in validation, although this was not focus of my work, this is what I recall on the topic.
[ii]- from amd's data sheet "The maximum power a processor draws for a thermally significant period while running commercially useful software. The constraining conditions for TDP are specified in the notes in the thermal and power tables."
NOTE! This source is old!!
That is wrong generally. Not sure how you got that idea either. The chips that overclock the highest are typically the most efficient ones, too. A 9900K that can run at 5.3 GHz at 1.35v is going to use less power than a 9900K that needs 1.5v to run at 5.3 GHz. At any frequency. Because the "golden" chip simply leaks less power, and needs less voltage at any given frequency. Lower TDP parts aren't special in any way, they just have lower clocks. If you limit the clocks on higher TDP parts, you get the same (or better) power consumption.
To drive the transistors in a chip you need to supply or sink enough charge so that the MOSFET will change state. The rate at which we can supply this charge places a fundamental limit on the switching speed of this transistor. Because until we overcome this charge requirement the transistor will not turn on/off.
Now the speed we can move this charge in and out of the input of the chip is governed by resistance. Higher resistance between VCC and the gate means it takes longer to over come the capacitance and change the state of the MOSFET.
Lets say for some given arbitrary Transistor its input capacitance is some 50pF , and lets also say our resistance to vcc is 10 ohm, then tao or the time constant is nothing but RC or 500 pico-seconds. In other words the maximum switching speed that we can see on the output is 1/tao or some 2Ghz. Now logic circuits are more than one transistor deep, and we can't reasonably run the circuit at exactly tao (Also at t=tao the gate is not exactly vcc it is ~.63vcc as this is an exponential function) and expect any level of signal integrity. But this tao is sort of a hard limit to switching speed as it is the time it takes the transistor to swap state.
In some sense low resistance is a boon. Low resistance means low tao, as tao is just RC. If tao is small than the transistor changes state more quickly. As a result for a given clock, the transistor has longer to overcome any inductance/capacitance present and is able to emit a cleaner signal.
But what lower resistance means is that you have higher power consumption as:
p=iv & v=ir -> P=V^2/R
So we see low resistance-> higher current. and higher current -> more power.
So we see it is a balancing act. We can have higher speeds or we can have lower power but not both. So if we are binning for a certain speed we are also binning for a certain power consumption characteristic. By selecting chips with speeds greater than XGhz we are also selecting chips with internal resistance < R.
Now what you said about over clocking is true. But because of an added twist.
Say we are binning a set of R that satisfy clk > XGhz. So naturally some subset of R will still be comfortably capable of XGhz while using less power than the average member of R. Now the chip has real limits to its capability to perform while hot. So this subset performs well as it is just low enough resistance to run a XGhz while limiting power use. On the high edge of the set R, we see chips that barely made XGhz and cant clock better. On the low edge of set R we see chips that are runing so hot as to barely maintain XGhz. So there is a sweet spot.
I think you're forgetting time in this equation. If two otherwise identical MOSFETs have different gate resistances, the lower-resistance MOSFET will charge faster and draw switching current for less time.
Take this all the way back to a simple linear circuit: a 1-ohm, 1-farad RC circuit will have a time constant of 1s, and if supplied with 1V the current will be I(t) = exp(-t). The power lost to heat in the resistor is then I^2R = exp(-2t), and integrated from 0 to infinity the net energy loss is 0.5J.
If instead the circuit has a resistance of 0.5 ohm, the resulting current is I(t) = 2exp(-2t). Power loss is I^2R = (0.5)*(4 exp(-4t)) = 2 exp(-4t), and integrated from 0 to infinity gives a net energy loss of again 0.5J.
In the meantime, the lower-resistance MOSFET is likely to save power from other effects. Most notably, faster switching implies the transistor spends less time in its linear region where it itself acts as a resistor between source and drain.
1 Ohm Case : P_res = integral exp(-2t) from 0 to tao -> .4323J
1/2 Ohm Case : P_res = integral 2*exp(-4t) from 0 to tao -> .4908J
Of course the effect diminishes greatly (to zero as you showed) as the switching time increases. But we are dealing with a great number of transistors switching very many times so the effect is still noticeable given timings are tight enough.
The thought on power savings as you mention is interesting but i am unsure off the top of my head of it.
If a transistor is only reciving 5v than it is fair to say the power consumed is equal.
But realisticly the input could change every clock cycle and we would see the cases vary.
The reason I only integrate to tao was to show if the input switches before t=infinity then a diffrence between cases clearly manifest. But as you say, when it does not switch for time t>>tao the diffrence is small.
It would be nice if any of the synthetic benchmarks included "10 hours of power-on, with 7 hours of web browsing, 2 hours of CAD, and a bunch of just-plain-idle time". Of course the choice of OS and mobo would matter a lot here too, but...
...I think it's entirely valid that idle power is probably a large part of power consumption and it's wholly ignored by current benchmark techniques. TDP is great for sizing heatsinks, but maybe I want to estimate my power bill.
SilentPCReview used to do a lot of this work, since heat means fans means noise. They'd have a "recommended system" every few months, which was the current performance-per-watt champion combo of CPU+mobo. I'm sitting in front of my last build from their 2008-era recommendation right now. But they're mothballed and I don't think anyone else has taken up that particular torch to run with it.
Because 1. a processor with a lower TDP doesn't necessarily actually use less power, at least not if your cooler can dissipate much more than the TDP, which it typically can.
And 2. because you can simply limit the clock speeds of any higher TDP CPU to reach any TDP you want. If you want a 35 W 3900X or 9900K, just set the clocks to whatever you need to reach 35 W max power usage, and you're done.
Of course the lower TDP parts are typically cheaper, so it makes more sense to buy those. But that's their differentiating factor, the price, not the TDP.
Not to mention that every slightly larger air cooler is a "passive cooler". Just don't connect the fan. Or set a fan curve that disables the fan as long as the CPU temperature is sub-62 C. Or 95 C, if you really don't want them to turn on.
As to running a larger air cooler without a fan. That’s heavily dependent on case airflow. High speed case fans really defeat the purpose of a passive cooler.
For something a bit more practical, if you're willing to get creative you can passively cool CPUs while getting fairly high performance too: https://www.youtube.com/watch?v=N-z9PidYH4E
Those are just NH-D15s, completely standard coolers with mounting brackets for pretty much every consumer socket out there.
PS: In terms of sacrificing performance, let’s agree to avoid the absurd. Or as the guidelines put it: Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith.
>Lots of closely spaced thin fins actually produce less cooling without good airflow.
That is true, however Noctua coolers tend to have a fairly big gap between fins, because they are designed for very low RPM use.
>In terms of sacrificing performance, let’s agree to avoid the absurd.
Not sure why you think it's absurd - the video just shows that there is no real minimum amount of cooling required anymore, at least with Intel CPUs. Obviously you're going to have to sacrifice some performance if you go passive only.
Although I'm not even sure anymore what we're even talking about. All consumer CPUs use the same sockets. All these coolers are available for every modern consumer or "pro-sumer" platform.
Motherboard’s use a small set of different mounting brackets for CPU coolers. But the physical CPU socket depends on several things including the physical size of the chip and thus the amount of surface area you want in contact with the the cooler.
In case you where unaware actually running a CPU at 100C will drastically lower it’s lifespan. You encounter similar issue if there are significant temperature differences across the chip. Which is why packaging includes a metal plate over the CPU even though it reduces cooling. However, this is a real tradeoff which means the contact area must be reasonably close to design spec.
For example, when introduced there was no aftermarket passive cooling available for the AM4 socket.
Really of the 5 considerations “Does it fit the mounting bracket?” is probably the least important. Fitting the motherboard and case are mandatory. Fitting the socket and TDP have a little wiggle room. However, with mounting brackets you can generally get something to work as long as you keep firm contact and it does not wiggle around it’s fine.
TDP would be useful if we standardized how it is measured, and at a whole systems level on standardized representative workloads.
Using an r5-3600 as a placeholder waiting for a 3950X. Was running an i7-4790k since that dropped, and wasn't unhappy with it, but there are things where it gets sluggish with the 4 cores, etc. I have definitely noticed the performance difference. Also jumped to Linux (Pop!_OS) from 2 years of hackintosh. I need to update to kernel 5.3 and update video drivers before swapping the older rx570, with an rx5700xt aftermarket.
Actually being able to order certain parts has been a bit of a pain though.
If you then compare the actual performance per watt, a 12 core CPU at 3.1 base / 4.2 boost pulling down approximately 65W is very impressive. Something similar from Intel (in terms of number of cores at even just the 3.1 base frequency) would likely have a TDP of at least 120W.
Closer, yes, but more useful? Both are off by a mile - not to mention that TDP isn't supposed to tell you a chip's maximum power consumption in the first place. It's supposed to tell you how good your cooler has to be to sustain base clocks / single core turbo, or in AMD's case, to sustain base clocks and some? boost clocks for a limited time.
>If you then compare the actual performance per watt
Performance per watt can certainly be interesting for many people. Performance per watt just isn't connected to TDP. The 3900X (105 W TDP) has higher performance per watt than the 9900K (95 W TDP). Probably at any frequency - although potentially the 3900X can't clock down as much. The 9900K can run Cinebench without a cooler after all (at least the 8700K can, so I'd suspect the 9900K can do that too), while the AMD processors can't. Also, the 3900 (65 W TDP) has the same performance per watt as the 3900X (105 W TDP), if you let them run at the same clock speeds.
The AMD power calculation is not "bit different", it's Intel who is cheating big time.
On a system with constrained power values, those who buy Intel will suffer a substantially higher hit than those who buy AMD.
I really, really don't see how. Both TDPs have very little connection to how much power the chips actually pulls at full load. 105 to 140 isn't useful in any way. If it was 107, sure, but 140 is 1/3rd higher than "spec" (I write "spec" because TDP isn't supposed to tell you what the highest power draw possible is if your cooling can dissipate more than the TDP in the first place, people just somehow seem to use it that way).
If you have a fixed TDP cooler, all you have to do is put that cooler on CPUs and see which ones will be faster. No looking at the specs required. If you have a fixed power consumption budget, but a better cooler, all you have to do is downclock until the CPU stays within that budget and then compare performance. Again, spec wasn't useful.
I care about TDP so I can estimate total power draw for my system when designing a custom build. I need to know about how big the PSU and UPS need to be, and getting a rough idea of electricity costs may influence my choices of components.
I can't trust the TDP figures and instead need to look up actual tests to know what it really draws, which is unnecessarily complicated.
The only honest TDP range they can give you would be: TDP between 10 and 300W.
I have a 9700K (95W TDP). At idle, the entire system consumes 30W at the wall. When running Prime95, the entire system consumes 250W, and that's undervolted. The 95W number is utterly useless. If I had bought a 95W capable cooler, the system would throttle under load.
I don't think they will gain any advantage with lying.
Still eagerly waiting for the r9-3950X though.