It has been a long time coming, but the pieces are slowly falling into place. Intel has now released the official Tjunction Max value for all 65nm and 45nm Core 2 processors at the Intel Developer Forum in Taipei.
ZoomIn a previous report on the August IDF presentation in San Francisco, Toms Hardware discussed how the information provided by Intel had very little real-world value. The reason Tjunction Max (the temperature where thermal protection is engaged) is not the silver bullet for 45nm Core 2 processors is because the sensors suffer from extremely high amounts of "slope error," that is, they become less accurate as the real temperature moves further from Tjunction Max.
An Intel document (PDF) describes the error on Atom processors, which use the same or similar DTS as those on 45nm Core 2 processors :
"The digital thermal sensor (DTS) accuracy is in the order of -5°C +10°C around 90°C ; it deteriorates to ±10°C at 50°C. The DTS temperature reading saturates at some temperature below 50°C. Any DTS reading below 50°C should be considered to indicate only a temperature below 50°C and not a specific temperature. External thermal sensor with BJT model is required to read thermal diode temperature."
According to Intel, if the actual temperature is below 50°C the temperature cant be trusted at all. With calibration, the slope error can be offset to an extent, but the reported temperatures will never be as accurate as those which are reported by the DTS on 65nm processors. Furthermore, the sensors can sometimes "stick," particularly at lower temperatures, and the worst of these sensors cant be calibrated properly.
Unlike their 45nm counterparts, the DTS for 65nm is much less affected by slope error, so that even a temperature readout that has not been calibrated can give a reasonably close representation of the actual temperature. The only major factor which will affect readings is Tjunction Max. Since the 65nm CPUs were released, enthusiasts and developers of temperature monitoring software have debated over the Tjunction Max. It was hoped that Intel would disclose these details at the August IDF ; however, we were to be disappointed. A few months later and Intel has finally decided to disclose the Tjunction Max for every processor in the Core 2 line, both 45nm and 65nm, as well as Xeon server CPUs. The Tjunction Max values for all Core 2 processors are as follows :
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Problems? See this thread at archive.org.)
