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Intel Core i7-860

We tested the power consumption of LGA1156 platforms with more than just a dual-core Core i3-540 processor. Intel offers not only dual-core but also extremely popular quad-core Lynnfield processors for this platform. Of course, we couldn’t disregard these CPUs that is why we included Core i7-860 into our today’s test session. Just like the Core i3-540, this processor also uses Nehalem microarchitecture, but is based on a monolithic processor die manufactured using 45 nm process. Moreover, this die contains not only four computational cores but also an 8 MB L3 cache, a dual-channel memory controller and PCI Express x16 graphics bus controller. The Lynnfield model we chose, Core i7-860, belongs to the upper mainstream price range that is why it supports Hyper-Threading technology and Turbo Boost. As a result, even though its nominal clock frequency is set at 2.8 GHz, it can overclock on its own up to 3.46 GHz depending on the operational load at a given moment of time.

In brief, the idea behind Turbo Boost technology implies that the processor clock frequency may be increased painlessly , if its heat dissipation doesn’t ever exceed the TDP. For our Core i7-860 CPU it is set at 95 W. However, when all four cores of this processor are fully utilized, the processor clock frequency is limited by 2.93 GHz.

Unfortunately, we can’t say how much power Core i7-860 processor actually consumes under maximum load, because its voltage regulator has the same peculiarities as the voltage regulators of all other LGA1156 processors. The total power consumption of a system equipped with this processor never exceeded 155 W in our tests. However, it is obviously more than the LGA775 system equipped with a quad-core processor consumed. Therefore, we have very serious concerns that Lynnfield processors in fact are pretty power-hungry.

During Core i7-860 overclocking we first of all disabled Turbo Boost, because the multiplier changes initiated by this technology lowered the maximum stable frequencies. However, once this technology was disabled, Core i7-860 multiplier could be increased by one point above the nominal value. We did use this option during overclocking, but later on we resorted to base clock adjustment. The maximum frequency for our processor to remain stable under maximum operational load was only 3.4 GHz (that was without any changes to its Vcore that stayed at the nominal 1.125 V). However, Lynnfield core responded very positively to core voltage increase, so that we could eventually push our overclocking maximum to the 4.0 GHz frequency, which is typical for 45 nm processor cores. All the settings used during our overclocking attempts are summed up in the table below:

All other voltages, which were not mentioned in the table, remained at their defaults. However, it is important to understand that these values aren’t universal. Processor dies differ from one another in their characteristics, that is why when you overclock different processors, you may need to play with slightly different settings.

The total system power consumption increased as the processor frequency grew higher. Take a look at the graph below:

It is a very illustrative picture, I should say. Up until 3.4 GHz, the system power consumption increases little by little, by about 4-6 W per every 200 MHz. It once again confirms our assumption that overclocking without involving processor Vcore adjustment doesn’t affect the system energy-efficiency that much. However, as we pass 3.4 GHz mark, things start to change dramatically. Every additional 200 MHz result into 30-40 W power consumption increase. And that happens only because we keep pushing processor Vcore 0.1 V higher every step of the way to ensure that the processor remains stable.

The currents graph shows an even more vivid picture:

When we hit 4 GHz frequency, Core i7-860 power consumption along the 12 V line reaches 180 W! But as you remember, this processor also receives some power from another 12 V line. In other words, Lynnfield processors can easily compete against Phenom II X4 965 in power consumption during overclocking. Here we also see some currents that exceed 15 A.

 
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