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Intel Core i7-4770K CPU Review - Intel Haswell For Desktop (Part 7)

9/8/2013 9:16:26 AM

Power consumption and heat dissipation

Haswell microarchitecture features many optimized solution for lower power consumption level so many people expect that Haswell CPU will help them saving more power. That expectation, actually, is not well-grounded. The Haswell can be used to create the mobile CPU which dissipates less heat compared to Ivy Bridge products. The ultra-low-voltage U and Y is a perfect example as it their TDP is just 15 watt or lower. However, a CPU design, which is optimized for low heat dissipation and power consumption, does not need to translate into an economical desktop CPU. Just like a practical problem, TDP of Haswell CPU for desktop is about 84 watts, which is 7 watts higher than the Ivy bridge series. It means that when working at typical speed of CPU desktop, Haswell requires higher voltage on specific CPU subunits. Moreover, Haswell is capable of controlling integrated voltage, as a power-hungry circuit needs large capacities for overclocking. That is why we have some knowledge about saving power of the premium CPUs of Intel.

In order to know more about the real power consumption level of Intel Core i7 4770K, we implement a round of special tests. The new digital units provided power from Corsair – AX760i – allow controlling power consumed and produced, which we use positively in our tests on power consumption level. The following charts (except for other regulation available), show the power consumed by the whole system (except for the monitor) measured after providing power. This is the total power consumption of the whole system. PSU’s effects are not taken into account. The CPU is loaded by running the 64-bit version of LinX 0.6.4 with AVX supported instructions. Moreover, we enable Turbo mode and all of the power saving related modes to have accurate measurement of power consumption level in idle mode: C1E, C6, Enhanced Intel SpeedStep and AMD Cool’n’Quiet.

Power consumed in idle mode

Power consumed in idle mode

Core i7 4770K system is very good in saving power in idle mode. The new power saving modes can be applied for desktops architectures, reducing the minimum power consumption.

Power consumption, 1 thread

Power consumption, 1 thread

Core i7 770K is less efficient in single-thread load, just equivalent to Core i7 3770K, and here the next chart comes.

Power consumption, 100%

Power consumption, 100%

It is a real shock! When the full load is executed, the Haswell requires a power level of 30 W, which is more than the Core i7-3770K configuration. Therefore, even though the low voltage CPU Haswell platform, which is used for the mobile devices, is economical, their desktop cousins are a different story.

Intel has optimized the microarchitectures of the super-mobile applications, but the Haswell desktop is not so efficient-per-watt. As we can see, not all of the Haswell desktops use the power in the proper way. Despite that, there is an issue that is required a carefully calculation. The Haswell’s power consumption and heat dissipation go up so quickly at full load which is generated by our LinX-AVX utility.

In the actual implementation, the Core i7-4770K is not that greedy as its predecessor. This means the power consumption of the CPU when it is encrypting the HD video with the codec x264.

Power consumption, x264 transcoding

Power consumption, x264 transcoding

Core i7 4770K reveals a higher power consumption level. However, we no longer mention the shocking difference of 30 W: it has just falls down to a few single digits.

Thermals and Overclocking

The Haswell and the LGA1150 platform change the overclocking procedure for two reasons. There are new divisors for the PCIe/DMI bus and there is now a built-in voltage regulator inside the CPU.

Overclocking feature

Overclocking feature

The first thing was expected because of the fixed correlation between the base clock rate and the PCIe/DMI clock rate used to make it impossible to overclock CPUs by raising the former. The PCIe/DMI bus doesn’t work properly when its frequency exceeds the default 100 MHz, so increasing the base clock rate to 105-107 MHz in order to render the LGA1155 platform nonfunctional.

This problem is solved to some aspects in the new Haswell processors. There are now a few methods that let you customize the base and PCIe/DMI clock rates not only as 1:1 but also as 5:4 and 5:3. Therefore, the LGA1150 platform can be stable at a base clock rate of 100, 125 and 166 MHz. All standard internal frequencies remain at their defaults in this case, but the x86 cores, the uncore part, the integrated graphics core and system memory get overclocked proportionally. It is also accepted if the LGA1150 CPUs with locked multiplier is overclocked, but only by 25% or 66% above the default frequency.

Haswell’s microarchitecture

Haswell’s microarchitecture

Only K series CPUs with an unlocked frequency multiplier allow you to complete overclocking freedom. By this way, during this the transition to Haswell, Intel added yet another bit to the processor multiplier register, so the maximum multiplier setting during overclocking has now reached 80x.

The integrated voltage regulator inside the CPU has an impact on the overclocking. The integrated regulator functions in a very special way. CPU’s voltage is used to minimize the high load, however the integrated regulator, would be automatically increase in this situation – above 0.1 volt even in the default mode. This effect is more likely to be recognized in the overclocking.

Unfortunately, this is a typical behavior of Haswell. You can only remove it by fixing the voltage at the default level, this, in another words, would disable every power-saving technologies. Thus, Haswell has provided an difficult option: you need to raise the temperature and heat dissipation of the CPU to a high level in order to execute the automatic increasing of the voltage inside the core, otherwise, you just completely ignore the power-saving mode when you are standing by.

But this is only one side of the problems. The Haswell is actually hotter than its predecessor. The maximum allowed heat of the CPU’s core is 100o C, but even in the nominal mode of the Core i7-4770K and there is high-performance air-cooler, its temperature has already reached the range 75-80o.

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