We leave the system to idle on the Windows 10 desktop for 5 minutes before taking a power draw reading. For CPU load results we run the Prime 95 in-place large FFTs test and take a reading after 5 minutes. The power consumption of our entire test system (at the wall) is shown in the chart.
The same test parameters were used for temperature readings.
I have had to remove the power consumption chart from this section due to the sporadic behaviour of the Kaby Lake CPUs while operating under Prime 95 in-place large FFTs load.
The i5-7600K would generally draw around 120W at its stock-clocked (MCT) load which dropped to 41W when idling. The stock i7-7700K drew 40W when idling (within margin of error of the 7600K reading) and increased to around 140W under Prime 95 load. These numbers were fairly consistent and the load value didn’t change significantly throughout the Prime 95 test period.
It’s when overclocking is thrown into the mix that power draw levels show unusual behaviour and rapidly change by significant margins.
The overclocked 7600K would draw 55W when idling and around 160W under load. But that load value would frequently jump as high as around 190W and then drop back down to around 160W before jumping back up again. Similar behaviour was observed with the overclocked Core i7-7700K which would idle at 56W but then jump between 160W and 190W under Prime 95 load (sometimes over 210W).
As a comparison, the stock-clocked i5-6600K operated at 38W idle and around 125W load and the stock i7-6700K was 42W idle and around 140W load. Overclocked to 1.35V, the i5-6600K operated at 55W idle and around 145W load and the 1.375V i7-6700K operated at 59W idle and around 170W load.
Temperature recordings were taken with the Corsair H110i GT CPU cooler’s fans running at full speed. Ambient temperature was maintained at 20°C. As was the case with power draw, I have had to remove the temperature chart from this review due to the sporadic behaviour of the Kaby Lake CPUs while operating under Prime 95 in-place large FFTs load.
The stock-clocked i5-7600K would generally idle at around 30°C and ran at around 60°C when loaded. The stock-clocked i7-7700K would generally idle at around 30°C and ran at around 70°C when loaded. Load temperature readings were generally consistent throughout the Prime 95 test run when the chips were at stock-clocked levels.
As was the case with the power draw testing, temperatures readings would spike by significant margins when the chips were overclocked and being tested using Prime 95. This makes perfect sense as higher power draw attributed to the CPU means more energy to dissipate which results in a higher operating temperature.
The 1.35V overclocked i5-7600K would generally idle a little over 30°C and operated around 70°C when loaded. But that load value was incredibly dynamic and would jump from around 65°C to as high as 85 or 90°C in very short periods of time (seconds). Similar behaviour was observed with the i7-7700K which would idle around 30°C then jump from around high-60s to as high as almost 90°C under Prime 95 load.
That represents a stability problem because those temperature readings were taken while using a Corsair H110i GT 280mm AIO cooler with its fans locked at full speed. In other words, we were using one of the best off-the-shelf CPU coolers on the market. A lower-performance cooler would have allowed the chip to hit 99°C and thermal throttle (as we observed when testing with 1.40V CPU VCore).
Our results tie in with the suggestion that replacing Kaby Lake’s TIM can significantly improve temperatures.
These issues look to perhaps be a potential bug with early motherboard BIOS revisions (we tested three different vendors’ boards) or the management engine software. It could also be the way in which Kaby Lake reacts to Prime 95’s extremely strenuous loading conditions. Whatever the issue, it is something that we will examine in the near future when release-level software revisions are available.
In the meantime, early Kaby Lake adopters are going to want to ensure that they use a high-performance CPU cooler when pushing into the realms of 1.35V and stability testing with Prime 95.