According to Intel, one of the major advantages of the finer 22 nm process used to manufacture Ivy Bridge generation processors is the lower heat dissipation and power consumption of the semiconductor dies. This is certainly reflected in the official third-generation Core i5 specifications: their TDP has been set at 77 W instead of the 95 W used previously. So, the new Core i5 will undoubtedly be more energy-efficient than their predecessors. But how big of an advantage will they boast in real life? Should we consider energy-efficiency of the 3000-series Core i5 processors a serious competitive statement?
To answer all these questions we performed a round of special tests. The new digital power supply unit from Corsair – AX1200i – 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-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.
When idle, the systems with all processors participating in our today’s test session consume about the same amount of power. Of course, the readings are not fully identical, the numbers differ by tenths of a watt, but we decided not to transfer them onto the diagram, because these insignificant deviations can most likely be attributed to the measuring error margin than the actual physical processes. Moreover, since all tested processors demonstrated very close power readings, the efficiency of the mainboard voltage regulator configuration starts to affect the power consumption levels, too. Therefore, if you are really concerned with the power consumption in idle mode, you should make sure that you have a mainboard with the most efficient voltage regulator circuitry design. As for the processor, our tests show that any LGA 1155 CPU could do just fine.
In case of single-threaded load, when the CPUs supporting Turbo mode boost their frequency to the maximum, we see noticeable differences in power consumption. First of all, we notice enormous energy appetite of the AMD FX-8150. As for the LGA 1155 CPU models, the ones using 22 nm semiconductor dies are really much more energy-efficient. The difference in power consumption of the quad-core Ivy Bridge and Sandy Bridge processors working at the same clock frequencies is about 4-5 W.
Full multi-threaded computational load increases the power consumption delta even more. A system equipped with a third-generation Core i5 is about 18 W more energy-efficient than a similar platform with a previous-generation CPU. So, desktop Ivy Bridge processors are simply unattainable in terms of performance-per-watt.