Living On The Edge (At Stock Settings)
Default Settings, Cheats & Heat
The first criticism, which we heard long before the launch, came from the direction of motherboard manufacturers. Typically, they'd take a normal closed-loop liquid cooler (they're scattered across the labs of these companies), slap it on top of a Core i9-7900X, and develop a BIOS that satisfies Intel's requirements and makes the board look good compared to its competition.
It didn't go down that way this time, though, and it sounds like Intel's rushed launch was to blame. None of the motherboards we tested ahead of the embargo behaved well. They all deviated from Intel's specifications in some way, from faulty P-states, incorrect Turbo Boost frequencies, and so much more.
But what struck us as most surprising was that every manufacturer had a skeleton in the closet. Let's compare the Asus Prime X299-Deluxe and MSI's X299 Gaming Pro Carbon AC (based on Thomas Soderstrom's testing). While Asus hits the brakes at stock settings, MSI leaves the power running full-tilt. Suddenly, the waste heat we were seeing makes a lot more sense.
Since Prime95 does not output any results, you need to be a bit more critical about where the differences in power consumption come from. To start, MSI has a BIOS entry called Enhanced Turbo, which is set to <Auto> by default, meaning it's active. In order to find (and disable) it, you have to open the Advanced BIOS menu and activate the Expert mode. Turbo Boost normally allows two cores to hit 4.3 GHz in lightly-threaded tasks, but with this switch in its default position, all cores are automatically pushed to 4.3 GHz under load. This is a nice factory overclock, which is of course stabilized by an automatic voltage adjustment.
At 4 GHz with Enhanced Turbo turned off, our CPU sucks down an astonishing 230W. The 4.3 GHz setting imposed by Enhanced Turbo mode looks a lot more conservative in comparison at 160W (with peaks just over 230W) under Prime95, curiously enough. This can be explained when you see Enhanced Turbo mode pulling clock rates back more sharply in AVX-heavy workloads.
Rendering with Cinebench, which doesn't utilize AVX instructions, changes this picture dramatically. The 4 GHz configuration consumes 145W for a score of 2169, while every core running at 4.3 GHz via "Enhanced Turbo" hits 190W for a modest jump to 2312 points. That's worrisome. You get a 6.6% performance benefit from 7.5%-higher clock rates at a cost of 31% more power consumption. Talk about a poor bang for your power/heat/cooling buck.
Checking VRM Temperatures
Let's get back to the voltage converters and test how our motherboard holds up under full load in the Core i9-7900X's default state, without any manual overclocking.
The two scenarios above presented us with a continuous load of 160W (slightly higher than Intel's rated TDP) and a direr 230W reading. That was the maximum we could generate using factory settings and our most demanding software. It's a worst-case scenario, to be sure.
Our comparison includes sensor data and an infrared-based analysis of thermal changes over 20 minutes.
Entry-Level: 160W+
According to our chart and video, the Core i9 is still in good shape thermally. A lot of that is owed to our high-end cooler. We also see that the package itself is already hotter than the maximum core temperatures. Testing with a compact all-in-one liquid cooling system yielded acceptable results still, but air cooling resulted in throttled clock rates after only a few minutes.
In places, the graph reveals consumption spikes up to ~230W. The CPU regulates the power requirement as it sees fit in order to prevent performance issues, though.
The motherboard's voltage converters handle this task easily; there is no reason to worry:
Ramping Up To 230W
Peak power consumption without overclocking reaches as high as 230W when we turn Enhanced Turbo mode off. The performance curve is much smoother, but our thermal readings are all much hotter. This applies to the voltage converters too, which work a lot harder under an almost constant load.
The motherboard's VRM is scratching at 90°C, but there's still a little headroom left. So long as we don't increase clock rates or voltages, we remain within our hardware's tolerances. It's just a little unsettling to be within 15°C or less of a VRM throttling event before any overclocking at all.
When it comes to gaming, the Core i9-7900X lands well under 100W. All that tells us, though, is that Skylake-X is useless for gaming-only. Graphics-bound titles simply do not utilize this chip's host processing resources fully.
Observation #4: Depending on whether you use the Enhanced Turbo option or not, power consumption in excess of 230W (in AVX-heavy workloads) or as high as 200W (without AVX) is possible right out of the box. That's no longer in the realm of air cooling. You need a good closed-loop liquid cooler at minimum. Even that's going to hit its limit, though, since the core temperatures peak at close to the point where thermal throttling begins.
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