The Stock Cooler Dilemma & Test Setup
The Stock Cooler Dilemma
Intel ships its multiplier-locked CPUs with basic thermal solutions. Although they are notoriously flimsy and usually pretty noisy, they've proven sufficient for cooling previous-generation models. That changes with Core i7-8700.
In the not-too-distant past, Intel's stock heat sink employed a copper core. More recently, however, the company switched to all-aluminum designs. That means Core i7-8700 comes with the same cooler as quad-core Kaby Lake-based Core i5s.
Frankly, we're surprised that Intel carried over the same heat sinks from those seventh-generation Core CPUs. Despite the -8700's 65W TDP, it's still based on a notably more complex die.
On paper, the -8700's 65W TDP fits nicely within the low-profile cooler's 73W rating. But remember that Intel specs the CPU's thermal design power according to its base frequency. Its chips actually exceed the TDP when they dynamically increase voltage and frequency through their Turbo Boost algorithms. As noted on Intel's Turbo Boost 2.0 informational page:
Note: Intel Turbo Boost Technology 2.0 allows the processor to operate at a power level that is higher than its TDP configuration and data sheet specified power for short durations to maximize performance.
According to our measurements, Core i7-8700 peaks at up to 126W during taxing all-core workloads. With that data in-hand, the stock cooler does appear insufficient.
While Intel guarantees base frequencies during normal operation, the company doesn't make promises about Turbo Boost clock rates because its processors only shift to higher P-states (pre-defined frequencies and voltages) when they're running below certain temperature, voltage, power, and current limits. Above them, the opportunistic algorithms are reigned in to keep the CPU in-spec.
As a general rule, Turbo Boost targets lower frequency bins as more cores become active. Intel does still advertise its maximum single-core clock rates, but it no longer divulges the multi-core clock rates (even though you can expose them through the company's XTU software).
|Intel Core i7-8700K||3.7 GHz||4.7 GHz||4.6 GHz||4.4 GHz||4.3 GHz|
|Intel Core i7-8700||3.2 GHz||4.6 GHz||4.5 GHz||4.4 GHz||4.3 GHz|
We've seen lots of speculation that Intel stopped disclosing multi-core Turbo Boost frequencies with Coffee Lake-based processors because its stock heat sink and fan couldn't fully facilitate those clock rates. Sure enough, a quick online search reveals several reports from owners claiming that their Core i7-8700s hit the maximum safe temperature of 100°C (TJ Max) during extended workloads. Once the processor reaches TJ Max, it throttles back voltage and frequency (along with power and heat) as a protection mechanism. Of course, throttling also results in lower performance.
Measuring The Impact
To investigate the claims, we observed a Core i7-8700 and its stock cooler during our x265 HandBrake benchmark. This real-world application is optimized to utilize all available cores. Moreover, it employs AVX instructions, which tend to increase power consumption considerably. We opened AIDA's system stability test window to monitor our -8700 during the workload.
As you can see in the second slide, Intel's cooler was quickly overwhelmed, causing the processor to repeatedly bounce off of its 100°C temperature limit and throttle performance to protect itself (charted in red in the lower window).
With the bundled fan manually set to 100% duty cycle, we logged frequency throughout our test run (first album image). Even with the thermal solution working as hard as possible, the -8700 regularly throttled back from its 4.3 GHz all-core bin into lower ranges.
We also monitored VRM temperature during the test to ensure our motherboard's power delivery subsystem wasn't responsible for the throttling. Those measurements landed within the range we expected.
Next, we ran the same test using a beefy Corsair Hydro Series H115i "Extreme Performance" all-in-one liquid-cooler. Manually cranking the two 140mm fans and pump up to 100% helped ensure that thermal output had no impact on our test results.
The difference is night and day. Intel's Core i7-8700 never exceeded 67°C, and the processor's frequency remained at a pleasingly-constant 4.3 GHz (though we did notice a few spikes higher during brief periods of lighter utilization). AIDA's system monitor confirmed that the CPU didn't throttle. Again, we see that our motherboard's power delivery subsystem satisfied the Core i7-8700's power and current requirements.
Comparing the difference between Intel's stock cooler (HS&F) and the all-in-one makes it clear that thermals clearly affect the -8700's performance. Turbo Boost is clearly designed to minimize the impact of thermal throttling: we only observe a 72-second delta over the course of our ~35-minute test.
A mere 3.4% separating those results may seem insignificant, but remember that we tested these configurations on an open test bench. A closed case would change the outcome almost assuredly. Also, we benchmarked at maximum fan settings, generating quite a bit of noise. It's far more common to use the motherboard's default fan curve, or to dial in an optimized fan profile that ramps up gradually. Unfortunately, those algorithms don't respond to control temperature fast enough to mitigate wild spikes and dips. As a result of the normal delay in fan speed adjustments, plus the less-than-ideal airflow in most PC cases, you could see larger slow-downs than what we recorded from a best-case test environment. This doesn't bode well for builders working with small form factors.
We did experiment with various thermal compounds between the stock cooler and heat spreader, but they didn't help much. Thus, we pin the negative outcome of our experimentation on Intel's paltry heat sink and fan combination.
Bear in mind that our benchmarks are run with the stock cooler and Corsair's all-in-one to highlight the difference in thermal performance. Some tests are short, while others take longer to complete. Some are single-threaded, while other are fully parallelized. Thus, the effects of heat influence each result in a unique way. As noted, we kept the fan speed at maximum and tested on an open-air bench, so our results represent a best-case scenario for Intel's stock cooler.
|Test System & Configuration|
|Hardware||AMD Socket AM4 (400-Series)AMD Ryzen 7 2700, Ryzen 7 2700X, Ryzen 5 2600X, Ryzen 5 2600 MSI X470 Gaming M7 AC2x 8GB G.Skill FlareX DDR4-3200 @ DDR4-2933, DDR4-3466Intel LGA 1151 (Z370):Intel Core i7-8700K, Core i5-8600K, Core i5-8400, Core i7-8700MSI Z370 Gaming Pro Carbon AC2x 8GB G.Skill FlareX DDR4-3200 @ DDR4-2400, DDR4-2667, DDR4-3466All EVGA GeForce GTX 1080 FE 1TB Samsung PM863 SilverStone ST1500-TI, 1500W Windows 10 Creators Update Version 1703 - All Spectre and Meltdown mitigations|
|Cooling||Corsair H115iIntel stock thermal solution (Core i7-8700)|
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