Although Core i7-2700K and Core i7-3820 are quad-core processors with very similar characteristics, based on the same microarchitecture and manufactured using the same production process, they have different thermal envelopes. LGA 1155 processors have a TDP of 95 W, while the new Core i7-3820 has a 130 W TDP. The main reason for this serious difference lies in the design differences between the two semiconductor dies: the quad-core LGA 2011 has increased number of the PCI Express lanes, larger L3 cache and quad-channel memory controller. And all though all of the above do not seem like significant factors, their combined contribution may be very noticeable. For example, if we compare the processors according to their die size and transistor count, then even a quad-core Sandy Bridge-E will turn out much more complex than a quad-core Sandy Bridge.
More transistors – higher power consumption. Let’s see what it means in actual numbers.
The graphs below (unless specified otherwise) show the full power draw of the computer (without the monitor) measured after the power supply. It is the total of the power consumption of all the system components. The PSU's efficiency is not taken into account. The CPUs are loaded by running the 64-bit version of LinX 0.6.4-AVX utility. Moreover, we enabled Turbo mode and all power-saving technologies to correctly measure computer's power draw in idle mode: C1E, C6 and Enhanced Intel SpeedStep.
We see a serious difference in power consumption even in idle mode. LGA 2011 system equipped with a quad-core processor consumes about 15 W more than a Core i7-2700K or Core i7-2600K based platform. Moreover, even an LGA 1155 processor overclocked to the maximum will be more energy-efficient in idle mode than Core i7-3820 working at nominal frequencies.
During overclocking, the quad-core LGA 2011 CPU eats up even more energy in idle mode than a six-core Core i7-3930K. However, it can be partially explained by a bug in the BIOS of Asus mainboards, which lock the processor Vcore once you increase the BCLK frequency and do not let the power-saving modes to fully kick in when the overclocked system is idle.
It is interesting to test the systems power consumption under single-threaded load because in this case all contemporary processors enable their Turbo mode, which boosts the performance while keeping power consumption and heat dissipation within acceptable range. Keeping in mind that the thermal envelope of the LGA 2011 processors is originally larger, their power consumption rate is again significantly higher than that of their LGA 1155 brothers.
Nothing changes in case of full CPU utilization. In the nominal mode Core i7-2700K consumes 25-30 W less than Core i7-3820, although their performance is very similar. In overclocked mode these two processors get closer to one another in power consumption, but we shouldn’t forget that the LGA 1155 processor works at higher clock frequency and therefore is faster. In other words, in terms of performance per watt quad-core LGA 1155 CPUs are way above Core i7-3820.