CPU not getting up to full TDP of 45W during prime95

lovro.zc · Jan 23, 2018

Hello good people of the forum!

I've recently cleaned and repasted my Asus laptop with i5-4200H and GTX850M. I repasted both using ThermalGrizzly Conductonaut liquid metal. I wanted to see the difference in CPU temps (which was massive after unclogging the vents and removing dry thermal paste) during a prime95 small FFT torture test. Everything works extremely well EXCEPT one thing that is bothering me.

During stress test I am monitoring temps with HWmonitor and below that the package power is indicated. I notice around 34-37W max power on the package and the cpu is rated at 45W. Intel XTU benchmark score remains the same before and after repasting, only the temperature changes.

Is better thermal dissipation making the CPU require less power? What's going on?

Thank you!

dudeman509 · Jan 23, 2018

No, it's just the instruction sets being used. Try a different Prime test.

Keep in mind the i7's use those same TDP numbers - it is just a threshold for cooling capacity, and HWMonitor is just doing an estimation, so you may not ever hit the full 45w number.

Bungle11 · Jan 23, 2018

the 45w rating is the max threshold for the chip as stated by the manufacturer. some chips don't need to reach 45w to achieve their maximum performance. Its called the silicone lottery. umlocked chips that can reach their 'out of the box' speed well below their rating tend to be better overclockers. if your chip runs at 3ghz @100 load max at 37w, it probably won't go higher regardless of stress test you run.

CompuTronix · Jan 23, 2018

lovro.zc,

On behalf of Tom's Moderator Team, welcome aboard!

lovro.zc :

dudeman509 :

Guys,

According to Intel's Product Specifications website, the i5 4200H is actually 47 Watts TDP: Intel® Core™ i5-4200H Processor -
https://ark.intel.com/products/75027/Intel-Core-i5-4200H-Processor-3M-Cache-up-to-3_40-GHz

Nonetheless, you're both partially correct.

Lower Core temperatures reduce leakage current, which in turn reduces Power (Watts), but only by less than 5%; not 17 to 24%, which is 8 to 11 Watts as shown above.

The key word in the term “Thermal Design Power” is Design. Factors include Microarchitecture, Core count, Core speed, Core voltage, Cache, Turbo Boost, Hyperthreading, Instruction Sets, Memory and IGPU. Faster processors naturally run hotter.

i5’s follow i7 Designs, while Pentiums and Celerons follow i3 Designs. Processors with Hyperthreading run hotter at the same TDP than those without, and processors with AVX Instruction Sets run hotter when executing AVX code than those without. This means at 100% workload, i7’s and i3’s may reach TDP, while i5’s, Pentiums and Celerons typically won’t. However, most overclocked processors will exceed TDP.

lovro.zc,

In your instance, although your 4th Generation "H" variant i5 Dual Core has Hyperthreading, and it's specified TDP is 47 Watts, it doesn't have the highest Clock speed in it's Family, and the IGPU isn't in use, both of which affect your measured TDP.

Q: Which version of Prime95 did you run? 26.6 is the correct version.

Later versions run AVX (Advanced Vector Extension) Instruction Sets, which typically causes unleastically high Core temperatures.

Incidentally, good job on your re-TIM with TG Conductonaut!

Once again, welcome aboard!

CT :sol:

lovro.zc · Jan 23, 2018

you seem to have extended knowledge of this topic, mr. "intel thermal specialist", so much that my ow has been extended too. thank you all fr very quick responses.

A: unfortunately I didn't pay atention to the version but I just took the latest prime95, I think it was 29.(something).

My brother is currently using the laptop, but I will retest with more normal test without AVX, although both tests (pre- and post-conductonaut) were done on same prime95 version and the difference was massive. from thermal throttling to 74°C.

P.S. can't wait to see what LM can do to a 7200U with undervolt

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