A few weeks back when we talked about the Intel i9-9900K here, we stated that it wasn’t a great value for money option also pointing out the thermal performance wasn’t in-line with a 95W TDP and that the processor drew more power than its rated TDP, significantly more.
Since then, there have been more revelations so before we delve into why this happens, lets clear a few things. TDP rating on a box isn’t indicative of a processor’s maximum power draw. Intel follows time limits such as the PL1, PL2 and PL3 standard. PL1 is basically for extended CPU run which is limited by the listed default TDP of the CPU, under normal conditions that is. PL2 ratings aren’t fixed by the listed TDP ratings, they are configured by Intel or OEMs to run on higher limits for a certain amount of time, till it hits the extended TDP rating. The PL2 rating of the i9-9900K is listed at 119W.
But as we have seen in several reviews, the i9-9900K hits 150W when all cores are under load, that’s 60% more than the rated TDP limit. So the guys at HardwareUnboxed found out that board makers weren’t limiting the i9-9900K by TDP, instead they were targeting the clock multiplier table. This way the TDP ratings are flouted for extended periods of time.
This gives a clearer picture on the issue. Intel states, the maximum frequency achieved on a single core of the i9-9900K will be 5GHz, but they don’t state the maximum frequency when all cores are active. Here you can see the i9-9900K can hit 4.7GHz under load with all cores active, with no caps on TDP.
But as soon as the 95W TDP rating is enforced, clock speeds with all 8 cores active drops significantly.
Here you can see the different TDP ratings in reference with the number of active cores. The i9-9900K hits the rated TDP rating with only 5 cores running at 4.8GHz. This hits a massive 153W with all cores running at 4.7GHz.
As HardwareUnboxed rightly points out
Essentially then Intel has two separate specifications for their high-end CPUs, a TDP limited specification that they loosely define or a clock multiplier table specification, and enabling one means it’s impossible to achieve the other. The TDP limit means you won’t reach the intended all-core clock speed while the clock multiplier table spec means you’re running well above the TDP.
Why Would They Do It?
Higher benchmark scores and good reviews really draw coverage. Both Motherboard manufacturers and Intel profit from this and if a board maker decides to enforce the listed TDP values, their numbers will obviously look bad on reviews.
It’s also misleading the buyers, because the i9-9900K doesn’t behave like a 95W processor, it runs quite hot on the stock cooler as pointed out by several reviewers. Both Intel and board makers should be more upfront and honest about these numbers, so people know exactly what they are getting with their hard earned money.
If you want to know more about PL1, PL2 etc and the issue at hand, I can highly recommend this article from AnandTech.