The Haswell microarchitecture lets Intel manufacture processors with surprisingly low heat dissipation and power consumption which are targeted at the mobile market. Desktop CPUs are a different story, though. The first thing we need from them is performance, so energy efficiency isn’t the main priority. In our tests of Haswell-based Core i7 CPUs, we found them to consume more power than their predecessors at high loads. This is indicated by the increased TDP (84 watts), which is 7 watts higher than before.
Anyway, the overall design of the LGA1150 platform suggests that we can expect better energy efficiency from it than from configurations built out of previous-generation components. A substantial part of the CPU voltage regulator resides in the CPU now, so the mainboard's power system is simpler. Then, the new chipsets are manufactured on 32nm tech process and consume 4.1 instead of 6.7 watts. That’s why we had some doubts that the high power draw of our Core i7-4770K configuration could be extrapolated to all other Haswell-based platforms.
Therefore, once we got our hands on the entire Core i5 processor lineup based on Haswell design, we decided to pay special attention to the power consumption of platforms built around them. The new digital power supply unit from Corsair – AX760i – allows monitoring consumed and produced electrical power, which we use actively during our power consumption tests. 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 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 utility with FMA instructions support (for AMD processors) and AVX instructions support (for Intel processors). Moreover, we enabled Turbo mode and all power-saving technologies to correctly measure computer's power draw in idle mode: C1E, C6, Enhanced Intel SpeedStep and AMD Cool’n’Quiet.
We see a familiar picture in the idle mode: the configurations with Haswell-based CPUs need considerably less power than their opponents.
The LGA1150 platform is quite economical when it comes to single-threaded loads. The new Core i7 and Core i5 CPUs need less power than their predecessors or AMD products.
At full load, the Haswell-based configurations require more power than their Ivy Bridge counterparts. The difference isn’t large at only 10 watts. It was larger in our earlier tests when we had engineering samples of CPUs, yet it is still a fact that Haswell CPUs need more power than the Ivy Bridge series at high loads notwithstanding all the power-saving measures taken by Intel. On the other hand, the new CPUs have become faster, so their performance-per-watt is actually comparable to that of their predecessors.