Guide to understanding Intel Temperatures

Guys, these forums have been fueled and fired up lately over discussions about temperatures. A lot of information is out there, and it's difficult to really get a clear sense of what is going on. While searching on the subject of appropriate Tjunction temperatures for mobile CPUs from Intel, I came across this interesting guide. It has some old info in it, but I think a lot of it is still relevant; http://www.techreaction.net/2009/10/14/guide-to-understanding-intel-temperatures/



Some interesting tibits;

Digital Thermal Sensor (DTS): Each core has its own DTS and this is where the Tjunction or core temperature reading is taken from. The DTS reports a relative distance to a fixed temperature (Tjunction Max) which must then be translated to an absolute temperature by software using the formula shown later in this post. This is usually called Distance to Tjunction Max or Delta to Tjunction Max. The primary function of the DTS is to regulate thermal protection mechanisms, not retrieve core temperatures.

The DTS is more accurate at temperatures closer to Tjunction Max and decreases in accuracy as temperature decreases.

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Tcase Max and Thermal Specification: Can be found on the Intel Processor Spec Finder. This is often confused by users as the maximum temperature for the cores, but in actual fact it refers to the maximum temperature that should be reached by the Tcase sensor. This specification is rounded to a relatively precise 0.1 C.

The only exceptions are mobile CPUs which do not have a heat spreader, where Thermal Specification refers to Tjunction Max instead and is rounded to the nearest 5 degrees.

Tjunction: Synonymous with core temperatures and calculated based on the output from the DTS using the formula shown further down in this post.

Tjunction Max: This is the maximum temperature the cores can reach before the PROCHOT# signal is sent and thermal throttling is activated, although throttling typically occurs a degree or two below this. In this post Tjunction Max refers to either the actual throttling point for a core/CPU or what is used by a temperature monitoring program.

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What Tjunction Max should I be using?

Many users stress over what value they should be using for Tjunction Max. Despite what most people think, Tjunction Max is not a fixed value for a whole range of CPUs like Intel makes it appear with Tjunction Target. It is subject to calibration error in the factory and has an undisclosed margin of variation (see “More information on Tjunction Max and DTS Calibration”). Tjunction Max can vary between individual CPUs and even between individual cores of the same CPU, particularly in Core 2 Quad CPUs which are Multi-Chip Modules, but also to a lesser extent in Core 2 Duo and Core i7.

Without thorough testing it is impossible to know exactly what Tjunction Max is for each core, nor is it particularly important. As I’ve said multiple times, the function of the DTS is to control thermal protection mechanisms. These trigger based on the DTS output (Distance to Tj Max), not the temperature of the CPU. Absolute temperature is completely irrelevant to proper functioning of thermal protection mechanisms.

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I find it to be interesting stuff. The fact that a lot of companies still use the old values to measure temperatures also tell us why it's likely that manufacturers use these older parameters which is different from the temperature probe measurement variables used by programs like speedfan, true temps and istats.

This does not prove anything, I just found it interesting though I also find some of it hard to understand.
Technology is an amazing thing. It really is amazing!

Brandon263 said:

My 2.3GHz Haswell MacBook Pro runs cool to the touch. It's actually kind of creepy, considering what my 2012 first generation rMBP was like. CPU heatsink is at 32 degrees celcius while GPU is at 36 degrees. Not to mention its faaaaast. Loving it.

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Good for you man! I hope mine won't have bad temps!^^