Some quick overclocking explorations
As is usually the case with every new generation of its chips, Intel is exposing some new knobs for overclockers both casual and extreme to toy with on Coffee Lake and Z370. The most prominent of these is per-core overclocking, a feature reserved for recent Broadwell-E and Skylake-X CPUs at the very least. Overclockers will also be able to tune a Coffee Lake chip's memory timings without a reboot. Extreme OCers will enjoy memory multipliers for speeds up to 8400 MT/s and better phase-locked loop (PLL) control.
We're not putting some of those more advanced overclocking features to work today, but it seemed criminal not to overclock our particular i7-8700K like a regular enthusiast might, given Intel's claimed process improvements. Because I like to live dangerously, I swung for the fences and tried for 5 GHz on all cores from the get-go. With a 280-mm cooler, it turned out a Blender-stable 5-GHz overclock was easy enough to hit, but I could never quite get Prime95 Small FFTs enough voltage to be stable at the same speed before we ran into thermal limits.
Eventually, I compromised and set a 5-GHz all-core speed with a -2 AVX offset, good for 4.8 GHz on all cores under AVX workloads. Incredibly, that configuration was happy even under Prime95 loads with an observed 1.284-1.296V using dynamic Vcore on our Aorus motherboard, so it wasn't difficult to cool at all— 80° C or so was the order of the day with a Corsair H115i on top. Those willing to delid their chips and apply more exotic thermal compounds would seem to have plenty of voltage headroom left to pursue even more extreme overclocks, assuming our particular chip isn't an exceptional cherry-picked example.
On the same note, we're finally giving one of AMD's Ryzen 7 CPUs a formal overclocked review. I picked our Ryzen 7 1700 to serve as the guinea pig for this article, and I was able to achieve 4 GHz on all cores with a pretty aggressive 1.41V with it. Thanks to AMD's use of solder under Ryzen CPUs' heat spreaders, though, thermals were never an issue under the AMD-supplied EK Predator 240-mm all-in-one I have on hand for Socket AM4 motherboards. My concerns about safe voltages and the limits of our given chip were much more relevant road blocks to higher speeds. Not bad for an eight-core, sixteen-thread CPU selling for $299.
I didn't stop turning up the clocks there, either. Intel's Sandy Bridge Core i7-2600K is rightly regarded as a legendary overclocker, so I pushed up the sliders on our particular chip and reached 4.6 GHz on all cores. With both stock-clocked and overclocked Sandy Bridge results in our stable, builders who have chosen to sit out Intel's incremental march of improvements over the past few years can see what they're missing.
Now that we've poked, prodded, tweaked, and tuned our test subjects, it's time to put up some numbers. Let's hop to it.
Our testing methods
As always, we did our best to deliver clean benchmarking numbers. We ran each benchmark at least three times and took the median of those results. Our test systems were configured as follows:
|AMD Ryzen 7 1700||AMD Ryzen 7 1700X||AMD Ryzen 1800X|
|CPU cooler||EK Predator 240-mm liquid cooler|
|Motherboard||Gigabyte Aorus GA-AX370-Gaming 5|
|Memory type||G.Skill Trident Z DDR4-3600 (rated) SDRAM|
|Memory speed||3200 MT/s (actual)|
|Memory timings||15-15-15-35 1T|
|System drive||Intel 750 Series 400GB NVMe SSD|
|Intel Core i7-2600K||Intel Core i7-3770K||Intel Core i7-4790K||Intel Core i7-7700K|
|CPU cooler||Corsair H110i 280-mm liquid cooler|
|Motherboard||Asus P8Z77V-Pro||Asus Z97-A/USB 3.1||Asus ROG Strix Z270E Gaming|
|Chipset||Intel Z77 Express||Intel Z97||Intel Z270|
|Memory type||Corsair Vengeance Pro Series DDR3-1866 (rated)||G.Skill Trident Z DDR4-3600 (rated) SDRAM|
|Memory speed||DDR3-1866 (actual)||3600 MT/s (actual)|
|Memory timings||9-10-9-27||16-16-16-36 2T (DDR4-3600)|
|System drive||Corsair Neutron XT 480GB SSD||Samsung 850 Evo 512GB|
|Intel Core i7-8700K|
|CPU cooler||Corsair H115i 280-mm liquid cooler|
|Motherboard||Gigabyte GA-Z370X-Gaming 7|
|Memory type||G.Skill Trident Z DDR4-3600 (rated) SDRAM|
|Memory speed||3600 MT/s (actual)|
|Memory timings||16-16-16-36 2T|
|System drive||Samsung 960 Pro 500GB|
They all shared the following common elements:
|Storage||2x Corsair Neutron XT 480GB SSD
1x HyperX 480GB SSD
|Discrete graphics||Nvidia GeForce GTX 1080 Ti Founders Edition|
|Graphics driver version||GeForce 385.69|
|OS||Windows 10 Pro with Creators Update|
|Power supply||Seasonic Prime Platinum 1000W|
Our thanks to Intel and AMD for all of the CPUs we used in our testing. Our thanks to AMD, Intel, Gigabyte, Corsair, Cooler Master, and G.Skill for helping us to outfit our test rigs with some of the finest hardware available, as well.
Some additional notes on our testing methods:
- You'll note that Intel's Core i7-6700K is missing from our results. We figured that the i7-7700K is a close enough substitute given its minor performance improvements over the Skylake chip—about 5%, on average. We used the time saved this way to test more overclocked CPUs and to explore use cases like streaming in more depth. We hope this is an understandable decision.
- Unless otherwise noted, we ran our gaming tests at 1920x1080 at a refresh rate of 165 Hz. V-sync was disabled in the driver control panel.
- For our Intel test system, we used the Balanced power plan, as we have for many years. Our AMD test bed was configured to use the Ryzen Balanced power plan that ships with AMD's chipset drivers.
- All motherboards were tested using the most recent firmware available from the board vendor, including pre-release versions provided exclusively to the press where necessary.
- All available Windows updates were installed on each test system before testing commenced. The most recent version of each software application available from each vendor was used in our testing, as well.
Our testing methods are generally publicly available and reproducible. If you have questions, feel free to post a comment on this article or join us in the forums.