I don't understand CPU power draw.

[Gat Pelsinger]

From the latest GN's video:

 

What happened to the 9900K and 10900K's power usage? First, the 9900K uses 93 watts on all cores, which is okay, but if you see the 7th line, that same 9900k overclocked just 300 MHz higher (oh wait, is that 5.1 GHz on all cores? Because the base 4.8 GHz is not on all cores, right (or is it? I am confused)? So, the overclock is way more than 300 MHz?) takes 100 watts more for such a slight overclock and a little bit more voltage! How? I don't get.

 

Second, the 10900k stock pulls 130 watts, but in the last line, that same 10900K, with slightly more voltage and I don't what overclock it is, because the clocks are within the stock turbo somehow takes almost 200 watts more. What is going on?

[Dukesilver27-]

Let's go back to junior high school physics for a sec, Power=Voltage*Ampere, so the more voltage, the more power.

Higher clock speed require more power to achieve stability, it has to do with the CPU's engineering design and efficiency.

Now, why does the higher CPU clock speed require more power to be stable? That I do not know exactly, and that is not your question.

 

[Electronics Wizardy]

I'm guessing the 9900k and some of those other parts are power limited, and sitting at their tdp. That doesn't say the actual clockspeed which is likely less. 

 

The newer parts have the power limits disabled by default on the k parts, but if you limit the power, it will use much less power.

[WoodenMarker]

As vcore and clock speed rises, CPU power draw scales exponentially and not linearly.

Here's a good example with the i7-2600k: https://forums.anandtech.com/proxy.php?image=http%3A%2F%2Fi272.photobucket.com%2Falbums%2Fjj163%2Fidontcare_photo_bucket%2FIntel%20Core%20i7-2600K%2Fi7-2600KVccversusDynamicPower-Consumption.png&hash=de1289ad274fd021b9e2b9fdc5aaa2d3

[Gat Pelsinger]

@Dukesilver27- @Electronics Wizardy @WoodenMarker

 

But what I was asking is that how the 9900K is taking so much power for such a little overclock? 93 at stock and 220 with just 300 MHz? Unless, it is actually not just 300 MHz, and that the 4.8 GHz stock is actually only single core, so it drops below 4.8 on all cores and GN overclocked to 5.1 on all cores, not single core, so it might be more than a 300 MHz overclock. Just need to verify.

 

Second, the 10900K is not even overclocked. In fact, it is a 100 MHz lower than the stock. The only thing that is listed that is increased is the voltage with just a little bump. But then how the heck is it drawing 316 vs the 130 stock?

 

If what @WoodenMarker said, then the 9900K overclock makes sense, but what about the 10900K? It is underclocked and with more voltage, which shouldn't more than double its power draw.

[unclewebb]

4 hours ago, Hensen Juang said:

the 10900k stock pulls 130 watts

The 10900K has a 125W TDP limit and the 9900K has a 95W TDP limit.

 

https://ark.intel.com/content/www/us/en/ark/products/199332/intel-core-i910900k-processor-20m-cache-up-to-5-30-ghz.html

https://ark.intel.com/content/www/us/en/ark/products/186605/intel-core-i99900k-processor-16m-cache-up-to-5-00-ghz.html

 

You cannot make comparisons if you do not know what the turbo power and time limits are set to in the BIOS. At stock settings, some motherboards will use the Intel default turbo ratio values and default TDP power and time limit values. Some motherboards cheat a little by including an all core overclock which is not part of the Intel specifications. Others boards cheat a whole bunch more by setting both turbo power limits to the max, 4095W, which is equivalent to unlimited. 

 

Some motherboards cheat a little by using some extra voltage to help improve stability. This can increase power consumption exponentially. 

 

1 hour ago, Hensen Juang said:

Unless, it is actually not just 300 MHz, and that the 4.8 GHz stock is actually only single core

Intel stopped publicly publishing any default turbo ratio data. ThrottleStop is able to read the default values that Intel has written to the CPU. Here is an example from a 9900K.  

 

 

The 9900K can use up to a 50 multiplier when 1 or 2 cores are active but this drops to 47 when all 8 cores are active. If the low power C states are disabled, which is a common thing for testers and enthusiasts to do, turbo boost will not work correctly. Disabled C states can limit the CPU to the 47 multiplier no matter how many cores are active.  

 

If a 9900K is set to its restrictive 95W TDP limit, performance and power consumption will be significantly reduced. 

 

It is impossible to make any sort of meaningful comparison if the test data does not include all of these details for each CPU and motherboard that is tested. Stock does not mean too much when talking about Intel CPUs. 

[Gat Pelsinger]

@unclewebb First of all, why did you tell me about the stock power of the 10900K? I was just asking that there is visibly no overclock done, just a bit more voltage (idk why the heck GN did that), and the power usage skyrocketed taking 316 watts, which is 200 watts higher than stock. With all my tech knowledge and experience, some overvolting shouldn't bring the power that high.

 

Second, for the 9900K, so basically in all core load even with the turbo limits removed, the clocks still drop? And then that 5.1 GHz is on all cores, so it did overclock MORE than 300 MHz, and that too on all cores? That is my understanding.

[NavyCobra1417]

power draw: (number of transistors)*(frequency)*(capacitance)*(Vdd^2)

 

Voltage for the transistor is squared, this is important. 

 

For transistors hit higher clock speeds, you typically need to increase the voltage.

 

Increasing cpu Voltage has an exponential effect on power draw as the voltage is squared.

 

Thus when overstocks are applied, often those last few hundred MHz require significantly more power. 

[Bagzie]

On 10/19/2023 at 5:55 AM, Hensen Juang said:

@Dukesilver27- @Electronics Wizardy @WoodenMarker

 

But what I was asking is that how the 9900K is taking so much power for such a little overclock? 93 at stock and 220 with just 300 MHz? Unless, it is actually not just 300 MHz, and that the 4.8 GHz stock is actually only single core, so it drops below 4.8 on all cores and GN overclocked to 5.1 on all cores, not single core, so it might be more than a 300 MHz overclock. Just need to verify.

 

Second, the 10900K is not even overclocked. In fact, it is a 100 MHz lower than the stock. The only thing that is listed that is increased is the voltage with just a little bump. But then how the heck is it drawing 316 vs the 130 stock?

 

If what @WoodenMarker said, then the 9900K overclock makes sense, but what about the 10900K? It is underclocked and with more voltage, which shouldn't more than double its power draw.

Because clock frequency doesn't scale in a linear fashion,  Its the same with GPU's.

 

15% more power on my 7900XT gives about 7% more performance.

 

The 7950X cpu for example doubles it's wattage for 5% more performance.

 

It's an exponential scale once you get beyond a certain point meaning you need much more amperage to achieve slight clock speed bumps.