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Core Temp Vs. Speed Fan - Which one is correct?

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Core Temp Vs. Speed Fan - Which one is correct?

Postby karmusjc » Mon Jul 26, 2010 1:57 pm

Hi,

I'm a long time user of the All CPU Meter gadget found at AddGadget.com which displays cpu usage and temps from a third party app. I recently downloaded their newest version of this gadget which uses Core Temp but the previous version used Speed Fan. After installing Core Temp and the new version of All CPU Meter, I was surprised to see that the temps displayed were 20°C higher than normal!!

So here's a screenshot with both apps side by side.

Image

My question is which one is right?
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Re: Core Temp Vs. Speed Fan - Which one is correct?

Postby The Coolest » Mon Jul 26, 2010 11:53 pm

The TjMax value, which is the reference point for temperature monitoring is not simple to detect on the Atom processor.
By specs, the TjMax is supposed to be 90C, but not all of the processors have such TjMax.
Core Temp takes it's best shot of guessing the TjMax correctly, but is not always right. For that reason Core Temp has temperature offset settings (Options menu).
Usually it's best to keep the processor at least 20C below the TjMax value while under heavy load. As long as you manage that, the "real" temperature is not important.

In your case, an offset of between -25 to -35 may be needed to give you correct and realistic temperature readings.
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Core Temp - Accurate temperature monitor for Intel's Core/Core 2 and AMD64 processors
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Re: Core Temp Vs. Speed Fan - Which one is correct?

Postby marieke » Sun Aug 29, 2010 10:57 am

Why does Core Temp report a temperature of 38°C where Speedfan reports 33°C ?
Both readings at same clock speed, mind you. Processor a bit overclocked and throttled.
If it just needs to read a Digital Sensor, which is so accurate ?
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Re: Core Temp Vs. Speed Fan - Which one is correct?

Postby The Coolest » Sun Aug 29, 2010 11:07 am

Both programs use the processor's integrated sensor, CPU temperature reported is basically affected by the TjMax value.
Core temp = TjMax - sensor value
In Core Temp the TjMax is 95c, in SpeedFan it must be set to 90, so the temps you see there are 5c lower.
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Re: Core Temp Vs. Speed Fan - Which one is correct?

Postby marieke » Sun Aug 29, 2010 12:24 pm

so the TjMax is not fixed, provided by Intel, for every one to know ?
Or SpeedFan is not up to date on the data maybe.
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Re: Core Temp Vs. Speed Fan - Which one is correct?

Postby The Coolest » Tue Aug 31, 2010 12:42 am

Intel has posted pretty solid numbers for their 45nm series CPUs.
They have also posted TjMax values for 65nm processors, but most of them were simply giving impossible readings. So for the 65nm chips, TjMax is mostly a guess.
I don't know where SpeedFan gets their values, I get mine from trial and error.
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Re: Core Temp Vs. Speed Fan - Which one is correct?

Postby mystere » Fri Feb 11, 2011 4:29 am

hello, I also wanted an explanation on the difference in temperature indicated by these three programs.
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Re: Core Temp Vs. Speed Fan - Which one is correct?

Postby The Coolest » Fri Feb 11, 2011 8:34 am

It's explained in section #7 of the FAQ
viewtopic.php?f=63&t=892
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