Intel TAT / CoreTemp / IDCC all different temperatures....

[unclewebb]

ted3: Sorry man, thats not throttling.

When I brought my E6400 up to 85C it was definitely throttling. On the Intel C2D there are two types of throttling.

http://www.intel.com/design/processo...als/253668.pdf
Here's a quote from page 13-5 of the Intel® 64 and IA-32 Architectures Software Developer's Manual, Vol. 3A:

"One mode modulates the clock duty cycle; the second mode changes the processor’s frequency. Both modes are used to control the core temperature of the processor."

When a C2D processor first starts to approach Tmax the duty cycle will be reduced from 100% to 87.5%, 75% and continuing down to 12.5% in 12.5% increments. If the temperature of the processor still can't be controlled then the second mode kicks in which reduces the processor frequency (MHz) like you experienced. The first "duty cycle" throttling happens approximately 3C or 4C before Tmax.

My testing has shown that CoreTemp 0.95 which uses a Tjunction of 100C for the E4300 is reporting the temperature correctly.

Rather than take a processor up to the boiling point I decided to do the opposite. I set out to try and run the processor as cool as possible.

To do this I dropped the FSB to 266 MHz ( 200 MHz for the E4300 ), I dropped the multi to 6X and then I also dropped the core voltage down to 1.175 volts. I booted up and set the Intel CPU fan at full speed to cool the processor as much as possible.

At idle I was able to get my E6400 down to 2C - 3C above ambient temperature which makes sense. A C2D puts out minimal heat at idle and even the OEM cooler is sufficient to dissipate that heat.

When I did a similar test on an E4300, CoreTemp 0.94 was reporting the core temperature significantly below ambient temperature which is impossible. An air cooled processor can't be running cooler than the surrounding air so this is a sign that CoreTemp 0.94 was reading too low.

By this test, the 15C correction introduced with CoreTemp 0.95 is correct for the E4300.

It would be interesting to see if anyone else can duplicate these numbers. This is the best and safest way I've found so far to prove that a software monitoring program is wrong.

CoreTemp 0.95 seems to be the most accurate program to date. If you don't believe the absolute value reported then just switch it to "Show Delta to Tjunction temp". I like to leave at least 10C to 15C of headroom to Tmax for maximum performance and stability.