core temp v real temp

ZigZag03 · Post by **ZigZag03** » Sat May 04, 2013 1:33 pm

searched this topic, hope this is not redundant. why do core temp and real temp display different temp numbers?

Post by **The Coolest** » Sat May 04, 2013 1:38 pm

Could you attach a screenshot? I can't answer such a question without knowing what CPU and differences in readings that are in question.

ZigZag03 · Post by **ZigZag03** » Sat May 04, 2013 1:45 pm

im not sure i know how to get a screenshot of the two side by side, but suffice to say that core temp is showing my cores all approx 5C cooler than real temp does, and if i ramp up the load that difference seems to hold true. not a big deal i guess, but made me wonder...

Post by **The Coolest** » Sat May 04, 2013 2:10 pm

You press on the PrintScreen key on your keyboard, and paste into paint. Then you can crop the image, and attach it here.

ZigZag03 · Post by **ZigZag03** » Sat May 04, 2013 2:23 pm

i dunno, man, i guess i have to take a lesson in printscreen, because pushing printscreen, shift-printsceen, alt-printscreen, ctl-printscreen, windows-printscreen, all do nothing, even with paint open. sorry, this is a topic for another forum. the 5 degree rule is still in effect, however, and i can only assume the two programs get or analyze their data differently. they report the same processor, same freq and load data, altho ct does load by core, while rt shows a single figure. like i said its not a big deal, just curious...

Post by **The Coolest** » Sat May 04, 2013 2:32 pm

Alright, what CPU do you have?

And after pressing printscreen, you go to Edit --> Paste in paint, or just press Ctrl+V. Should work unless your printscreen key is remapped as something else which is unlikely.

ZigZag03 · Post by **ZigZag03** » Sat May 04, 2013 5:44 pm

ok sorry, made it work this time...

Post by **The Coolest** » Sat May 04, 2013 6:38 pm

Nice.
The reason you have a 5C difference is because Core Temp and Real Temp assume different TjMax values for the CPU.
The TjMax is a reference point which is used to calculate the actual core temperature. Core Temp assumes it is 85C, Real Temp assumes 90C.
TjMax on the Core 2 series, especially the 65nm variety wasn't known and mostly based on the values inherited from the older Core series. There was no concrete data by which to go by, so most of the applications out there that read core temps are making their best guesses when deciding on a TjMax value.

ZigZag03 · Post by **ZigZag03** » Sat May 04, 2013 6:51 pm

forgive me but i don't really get that. so temp is not a real measured metric but something calculated from an arbitrary max temp?

Post by **The Coolest** » Sat May 04, 2013 7:10 pm

In short, yes. But 85C or 90C it is pretty close to the real value.
Only Core iX series have a pre-programmed TjMax value, which means that there is no more guessing about what that reference point is.

ZigZag03 · Post by **ZigZag03** » Sat May 04, 2013 7:15 pm

ok we are not going to beat this poor horse any further, but what youre saying is that we don't really know exactly what the actual temps are, because there is no way to measure them directly. yes?

Post by **The Coolest** » Sat May 04, 2013 7:20 pm

What Core Temp and others measure is the delta from the TjMax value.
Meaning the temperature = TjMax - 'value read from CPU'.
It works that way for all of Intel's processors, only in the older ones, the TjMax wasn't 100% known.
So no, we don't know the absolute temperature with a 100% accuracy on these chips.

ZigZag03 · Post by **ZigZag03** » Sun May 05, 2013 12:53 am

i get it now and thank you very much for being so patient with me.

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core temp v real temp

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