Report: Skylake-X CPUs prove hard to cool thanks to TIM change


— 12:21 PM on July 10, 2017

Intel's launch of its Core X high-end desktop CPUs and the accompanying X299 platform has seen some controversy in overclocking enthusiast circles. The mish-mash of architectures, core counts, memory configurations, and PCIe lane allowances on the X299 platform has been the source of confusion ever since Intel's announcement, and complaints about apparent high system power draw and underspecced voltage regulation on X299 motherboards started soon after demanding overclockers got their hands on the first wave of boards. Igor Wallossek at Tom's Hardware rigged up a Core i9-7900X CPU and an MSI X299 Gaming Pro Carbon AC motherboard for a closer look at what happens when that gear is pushed to the limit.

The main takeaway is that cooling Intel's Core i9-7900X is a tough task even at stock clock speeds, even with a high-end Alphacool Eiszeit 2000 refrigerating cooling system. The site recorded a 71-Kelvin difference between the chip's core temperatures and the temperature at the top of its heat spreader under load, even with that exotic cooler at work. Tom's Hardware attributes this behavior to Intel's decision to abandon the practice of soldering the integrated heat spreader (IHS) onto the CPU die in its range-topping desktop chips. That move could be seen as disappointing in light of the high price tags attached to most members of Intel's Core X CPU lineup, and when considering the fact that (to our knowledge) rival AMD solders the IHS onto every Ryzen chip it produces.

The sheer power dissipation of the i9-7900X is another obstacle to proper cooling. The chip dissipates 160W under a Cinebench load using Tom's Hardware's testing configuration, and running the Prime95 Small FFTs torture test pushes those figures to 230W. The Cinebench load pushed VRM temperatures to 73° C, while Prime95 Small FFTs caused the VRMs to reach about 90° C. For reference, the site reports that its MSI motherboard will begin throttling the system when the thermistor near the VRMs hits 105° C. In either case, the site recommends at least some kind of beefy all-in-one liquid cooler to properly cool the chip. Even with Cinebench, Tom's observed thermal throttling from the i9-7900X with an air cooler on top.

Overclocking the chip only worsens these challenges. The i9-7900X dissipates nearly 250 W under the AVX-enabled Prime95 at a 4.5 GHz overclock. A test at 4.6 GHz running LuxRender again resulted in a 250 W power draw. In this scenario, the CPU started throttling before the VRMs even got toasty. The site soldiered on and pushed the 7900X to a 300W power draw anyway. After 10 minutes, the VRMs reached 105° C and the system went into a thermal throttling loop.

The range of X299 motherboards did not escape Wallossek's ire, either. He complains in the article about flaws in every board manufacturer's X299 wares, "including faulty P-states, incorrect Turbo Boost frequencies, and so much more." He goes on to detail inconsistencies in the way the MSI X299 Gaming Pro Carbon AC handles Turbo Boost and how these inconsistencies lead to higher-than-expected power consumption. While we're still developing full impressions of the X299 platform, we doubt our testing will be free from similar challenges. Overclockers and system builders alike will need to be fully aware of the demands of Skylake-X when planning an X299 build.

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