Intel Core i7 "Nehalem" 920, 940 & 965 XE Processor Review

Although the Core i7 series is manufactured with the same 45nm process as current Core 2 processors, each microarchitecture has unique thermal characteristics and power consumption figures. There is no doubt that Intel has focused on energy-effiency this new microarchitecture, but they have also added a significant number of new performance improvements features that generally increase power consumption.
With this in mind, let's take a closer look at the Core i7 series power consumption and thermal output.


Power Consumption

For our power consumption test, we enabled all the Intel energy saving features in the BIOS, then let the system idle for 15 minutes and measured the peak wattage through our UPM EM100 power meter. We repeated the same procedure for 15 minutes of Prime 95 Blend load. Here are the results:


The results are pretty much what we expected. Under load, the Nehalem architecture has higher power consumption than Penryn does, and this despite having over 10% less transistors. The reasons for this higher power consumption are the integrated memory controller and built-in QPI Link. Both of these new core components are quite power-hungry, especially under full load scenarios. Having said that, you must take into account the simple fact that Nehalem does more work per clock than Penryn does, and when viewed from that perspective, Nehalem is in fact a more efficient design when it comes to Performance per Watt.

On the idle front, the situation is quite promising. For example, the Core i7-965 uses 13% less power at idle than the identically-clock QX9770, which is a noteworthy achievement by any measure. All three Core i7 series processors recorded identical idle power consumption figures because they all downclocked to approximately 1536Mhz (128Mhz x 12).

Clearly, the Power Control Unit (PCU) is doing a good job of dynamically lowering the voltage and frequency of the CPU cores, or perhaps even using the Power Gates technology to completely shut down and place in a C6 sleep mode some of the idle cores.


Temperature Testing

For the temperature testing, we had both the stock Intel Core i7 CPU cooler and a Thermalright Ultra-120 eXtreme with an LGA1366 mounting kit to test out. OCCT v2.0.0a was run for 15 minutes and the temperatures were recorded at 5 minute intervals and the results averaged out. We relied on the new CoreTemp 0.99.3 utility to accurately report temperatures. The ambient temperature was 21°C/71.6°F.


As you can see, and Intel effectively told us, the stock Core i7 cooler is not intended for the high-end 965 model. However, it is capable of keeping the other two models at fairly respectable load temperatures. The venerable Thermalright Ultra-120 eXtreme was much better at cooling these new processors, and even the high-end 965 is reigned-in a great deal. As usual, those interested in serious manual overclocking will want to invest in a good quality cooler.