Temperatures and Power Consumption

Now that we have checked out the overclocking potential of the new Wolfdale CPU on E0 processor stepping, it will be extremely interesting to see how its thermal and electrical characteristics have changed compared with the predecessors. To answer this question we compared the power consumption of systems (without the monitor) built around Core 2 Duo E8500 with C0 processor stepping and Core 2 Duo E8600 with E0 processor stepping.

We measured the system power consumption in three states. Besides our standard measurements at CPU’s default speeds in idle mode and with maximum CPU utilization created by Prime95, we added one more test. It was performed with 100% CPU utilization when both processors were overclocked to 4275MHz frequency obtained as 9.5 x 450MHz FSB. To ensure that the testing conditions are absolutely identical we set the Vcore for both processors at 1.4V. We activated Enhanced Intel SpeedStep and Enhanced C1E Halt State power-saving technologies during these tests.

As you can see from the obtained results, the new E0 processor stepping can also boast lower power consumption. Core 2 Duo E8600 under workload consumes the same amount of power as Core 2 Duo E8500 with 166MHz lower frequency. The results for overclocked processors show the advantage of the Core 2 Duo E8600 newcomer very clearly: the system with new E0 processor stepping consumes 9W less power than the one with its counterpart with the same Vcore and frequency settings. This is more than convincing.

During our tests we noticed that the thermal sensors of the CPU with new E0 stepping act differently. In idle mode and under maximum workload Core 2 Duo E8600 temperatures were very different from what our test Core 2 Duo E8500 with C0 stepping would demonstrate in the same conditions: they were higher. To illustrate our words here are the temperature diagrams according to the built-in thermal sensors from the first core. The results were obtained during a 15-minute run of the OCCT stability test for both processors overclocked to 4275MHz.

Click to enlarge

Click to enlarge

As you can see, overclocked Core 2 Duo E8600 reports higher temperatures in idle mode and under workload. However, it evidently contradicts the lower power consumption of the new CPU. Therefore, there could be only one conclusion: the diagnostic utilities algorithms need to be adapted for the new implementation of the PECI protocol mentioned among the features of the new E0 stepping.

It could be the fact that digital thermal sensors in the processor cores do not report absolute temperatures, but the difference between the current and maximum safe processor temperature – Tjmax. This Tjmax parameter is not documented anywhere for desktop Core 2 processors, but the utility developers assume it equals 105ºC, judging by the same parameter of the mobile processors. However, looks like new Wolfdale processors with E0 stepping have a different Tjmax value, so the utilities end up reporting higher readings. It is important to keep in mind this peculiarity of the new CPUs.