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Power Consumption and Heat Dissipation

The Haswell microarchitecture featuring a lot of optimizations for lower power consumption, many users expect Haswell-based CPUs to make desktop PCs more economical. Such expectations are not well-grounded. The Haswell can indeed be used to create mobile CPUs that dissipate less heat than Ivy Bridge products. The ultra-low-voltage U and Y series with a TDP of 15 watts and lower are an excellent example. However, a CPU design optimized for low heat dissipation and power consumption doesn’t necessarily translate into an economical desktop CPU. As a matter of fact, the TDP of desktop Haswell-based CPUs is 84 watts, which is 7 watts higher compared to the Ivy Bridge series. It means that making the Haswell work at clock rates typical of desktop CPUs requires high voltage on certain CPU subunits. Moreover, the Haswell features an integrated voltage regulator, a power-hungry circuit which should have a large reserve of capabilities for overclocking. That’s why we have some apprehensions about how economical Intel’s new flagship CPUs are.

To find out more about the practical power consumption of Intel Core i7-4770K processor we performed a round of special tests. 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 AVX instructions support. 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.

The Core i7-4770K system is very economical in idle mode. The new power-saving states can be applied to the desktop infrastructure, lowering the minimum level of power consumption.

The Core i7-4770K is less efficient at single-threaded load, becoming comparable to the Core i7-3770K. And here’s the next diagram.

That’s a shock really! At full load the Haswell-based system needs almost 30 watts more power than the Core i7-3770K configuration. So, even though low-voltage Haswell-based CPUs for mobile gadgets are very economical, their desktop cousins are a completely different story. Intel has optimized the new microarchitecture for ultra-mobile applications but the desktop Haswell is no good in terms of performance per watt. Not all Haswell-based CPUs are energy efficient, as we can see.

There is one thing that should be taken into account, though. The Haswell’s power consumption and heat dissipation go up rapidly at full load which is generated by our LinX-AVX utility. In real-life applications the Core i7-4770K isn’t as voracious as it seems in comparison with its predecessor. Here’s the power consumption of the CPUs while encoding HD video with the x264 codec.

The Core i7-4770K demonstrates higher power consumption than Core i7-3770K. However, we are no longer referring to a shocking difference of 30 W: it has dropped down to just a few single digits.

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