CPU Reviews System

Skylake-X review: Intel Core i9-7900X and the X299 platform

Introduction Intel's new X-Series consists of i5, i7, and reissued i9 processors, all of which require the same X299 chipset that comes with the LGA2066 socket. The S-series processors will continue to be used with the 200 chipset. In some applications and games, we've encountered performance trends that didn't match our expectations. Considering that Skylake X has a speed advantage due to higher clock speeds as well as new architectural... Intel has reduced the shared Last Level Cache (LLC-L3) and transferred it from an inclusive to a non-inclusive (but exclusive) approach. This was done with the help of an efficient caching algorithm that improves the hit rate of the L2 cache ... The Basin Falls X299 chipset The Kaby Lake-X and Skylake-X processors sit in an LGA2066 socket (R4), powered by an X299 chipset with 6 watts of power, underscoring Intel's strategy of using server chipsets for their HEDT- Li... Why should it always only hit AMD when a change of architecture leads to application-specific "collapses" in the expected performance or, more simply put, the CPU in certain applications simply does not... Ashes of the Singularity: Escalation Because we were just so nice, we continue the high-altitude flight of the overclocked Core i7-6950X, because even with this benchmark the optimization problem described above is very clear:... Grand Theft Auto V (DX11) GTA V restores the old pecking order and also shows two things. First, it's still an Intel domain, but AMD has made up for it with the Ryzen CPUs! It's really amazing how to deal with some fine... Project Cars (DX11) Even with Project Cars, the chemistry between the new CPU and the engine is right, even though it was observed time and again that all 10 cores clocked up to 4.0 GHz, even though they were not all busy. But we would... Introduction During the launch article of AMD's Ryzen 7 CPUs, we had already explained all workstation and HPC benchmarks in great detail and also questioned the background for many results in some cases even down to the last detail. En... Important preliminary remark Since Intel no longer realizes the contact between Die and Heatspreader by metallic solder at Skylake-X and Kaby Lake-X, but also uses cheaper TIM (Thermal Interface Material) to use the same way. Cooling with the Chiller crowbar In order to be able to achieve usable (overclocking) results, we had to switch from the normal water cooling to the Alphacool Ice Age Chiller 2000, as already mentioned in the previous chapter. ... What is left for us after all these pages as a summary? Intel's market leadership in recent years is ultimately based on a continuous offer of more or less large updates, which of course also this time a certain amount of expected...

Cooling with the Chiller crowbar

In order to be able to achieve usable (overclocking) results, we had to switch from the normal water cooling to the Alphacool Ice Age Chiller 2000, as already mentioned in the previous chapter. Trials with AiO compact water cooling systems such as a Corsair H100i and the Enermax LiqTech 240 were already running into the thermal limit at the standard clock and Prime95, while the custom loop cooling later failed at 4.6 GHz.

But stop! Normally, should such cooling solutions be able to cool such a CPU sufficiently? After all, we were able to operate the Core i7-5960X at 4.8 GHz and a normal AiO compact water cooling system, although even then up to 250 watts of power consumption were recorded. In the end, however, we were simply forced to force a constant 20°C in the cooling circuit in order to be able to do any experiments at all!

High delta values as a cooling trap

The real reason is Intel's incomprehensible fun brake in the form of inappropriate (but arguably much cheaper) thermal paste instead of a sensible solder. However, since the DTS (Digital Temperature Sensors) at Intel only started at approx. 35 to 40°C provide reasonably resilient values, we have changed our view in this way and only recorded values above in the first evaluation. In order to be able to correctly classify the misery with the thermal paste, we now show the temperature differences between the constant 20°C cool water block and what we have determined as CPU temperature from the sensor values.

The following curve shows extremely clearly that the waste heat can only be dissipated poorly and insufficiently. What just worked like this with a thermal 100-watt bread roll like the Core i7-7700K, however, now leads the paste strategy into the absurd. We also measured the temperature of the heat spreader using our own, very thin copper plate, analogous to the Ryzen launch article, whereby the delta determined here later flows into our individual curve.

At the end, the following curve thus represents the temperature differences between the heatspreader top and the calculation cores, whereby the results have shocked us:

Although with our Chiller, the Alphacool XPX water block and the Thermal Grizzly Kryonaut thermal paste we have used pretty much the best and most expensive that the market has to offer, at the end there are a whopping 71 Kelvin as the temperature difference between the temperature of the cores and top of the heatspreader on the bill! This is especially annoying in that it makes normal cooling solutions look quite silly at full load and factory cycle. AMD has impressively demonstrated how to better disprove such power consumption values with Ryzen 7, even if we were upset with the artificially offset output values of the X-models.

In order to illustrate our incomprehension, we now have the temperature gradients in detail, as they are out-of-the-box with Prime95 or Prime95. Luxrender, packaged in a diagram. It is reasonably logical that the Chiller or a proper conventional custom loop cooling system still work well here, but any other cooling solution is already being pushed to the limits with these loads. Even the motherboard manufacturers have told us about the onset of the aiO compact water coolers used when Prime95 is released without an AVX choke.

Up to 65°C Tcore at a heatspreader temperature of approx. 24°C already results in a delta of more than 40°C. We reached this value with a power dissipation of just under 230 watts. However, as soon as you move above the 300-watt limit, which you can even use with simpler rendering programs from approx. 4.6 or 4.7 GHz and the necessary voltages (depending on the chip quality), hardly anything goes with the Chiller. With the maximum values of just over 300 watts we have achieved, the CPU is already running permanently thermal limit of 100°C, shortly afterwards there is a logical shutdown.

Leakage

We measured the power consumption values with identical load and different cooling solutions, whereby we have of course set physical limits here. The increase in leakage currents at higher temperatures is kept within a very manageable framework, as shown by the next curve. The power consumption increases by a total of 5% when the core temperatures increase by approx. 40 Kelvin. This is more than just acceptable, but really good. The measured values above approx. 95°C, however, are already somewhat inaccurate due to the onset of throttling. For once, we worked with a low-pass filter that smooths the short break-ins to some extent.

Intermediate conclusion

Yes, it could have been so beautiful if it wasn't for the trouble with the thermal paste between heat spreader and Die. Well, the normal user in the semi-professional area will hardly overclock the CPU, which is likely to significantly reduce the mourning community. But even reasonable users of the Core i9-7900X will not be able to avoid investing at least in a clever cooling. Whether you then use a really good AiO compact water cooling or better use a proper water cooling, let's face it. Air cooling is eliminated in full-load operation, especially in summer.

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About the author

Igor Wallossek

Editor-in-chief and name-giver of igor'sLAB as the content successor of Tom's Hardware Germany, whose license was returned in June 2019 in order to better meet the qualitative demands of web content and challenges of new media such as YouTube with its own channel.

Computer nerd since 1983, audio freak since 1979 and pretty much open to anything with a plug or battery for over 50 years.

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