Core i7-8700K Review: Coffee Lake Brews A Great Gaming CPU

Intel Brings More Cores

Intel’s Core 2 Quad processors debuted with four cores in 2006. Although six-core models landed four years later in the high-end desktop space, the company’s most accessible chips topped out in quad-core configurations for more than a decade. The Coffee Lake era begins with Intel upending its mainstream line-up by adding two more cores to Core i7, i5, and i3 families. Call this a much-needed improvement, cleverly timed to stave off AMD's core-laden Ryzen assault.

Of course, while Intel's accelerated Coffee Lake-S launch makes it look today's unveiling is a direct response to heated competition, in reality, the long incubation period for new processors means it’s more likely the result of 10nm manufacturing delays.

Just last year, Intel announced a new process-architecture-optimize cadence designed to deliver smaller transistors every third generation. That's a profound departure from the glory days of Intel’s tick-tock model. The latest 14nm++ process is the fourth outing of the 14nm node, which originally debuted with Broadwell back in 2014. So, it appears that PAO is already falling by the wayside. In the days of tick-tock, we'd also be talking about a new architecture right now. But Coffee Lake employs the same Skylake design as Kaby Lake before it. We also get the same fundamental integrated graphics engine found in the previous generation. To be sure, Coffee Lake is another iterative update.

But there’s nothing mundane about adding more cores. Intel claims Coffee Lake offers up to 25% more gaming performance and up to 45% more “mega-tasking” performance. Given similar price points versus Kaby Lake, we're almost certainly looking at a huge step forward in value.

This is obviously a busy year for Intel. But as if the company's product stack wasn't already confusing, its eighth-generation portfolio draws from three separate architectures, including 14nm+ Kaby Lake-R (refresh), 14nm++ Coffee Lake, and 10nm Cannon Lake, which should land next year.

Intel Core i7-8700K

Core i7-8700K serves as this generation's flagship, sporting six Hyper-Threaded cores. Already, that's a big increase from Kaby Lake's 4C/8T maximum. It features the company's highest clock rates, accelerating up to 4.7 GHz via Turbo Boost. The -8700K does sacrifice some base frequency in exchange for a higher core count, though. Its 3.7 GHz specification is 500 MHz lower than the -7700K, offsetting the increased power consumption and heat generated by a 6C/12T configuration.

The -8700K's Coffee Lake design utilizes a 14nm++ process, which Intel claims offers 26% more performance and 52% less leakage power than first-generation 14nm manufacturing. Those advances enable the higher Turbo Boost bins and reduce consumption enough to carve out room for extra cores. A more complex die does necessitate a TDP rating of up to 95W. But that's only 4% higher than Core i7-7700K. And as we've seen before, Turbo Boost allows the CPU to operate beyond its rated TDP as long as current, power, and temperature fall below specified limits. As you might imagine, then, the impact of two additional cores is felt under load.

The top 4.7 GHz Turbo Boost bin should help improve performance in lightly-threaded applications. But Core i7-8700K also includes aggressive multi-core bins to help chew through threaded workloads. Because these CPUs employ Intel's Skylake architecture, we aren't expecting any speed-ups attributable to IPC throughput. All gains come from core count and clock rate alone. Intel isn't officially disclosing a die size or transistor count, but early delidding efforts indicate a ~151mm² area. That's naturally larger than Kaby Lake's ~122mm², reflecting the additional execution and cache resources. Intel confirms that Coffee Lake continues to employ its ring bus, rather than Skylake-X's mesh topology.

Intel also adds 50% more cores to its Core i5 family, and doubles Core i3's core count. But it pulls Hyper-Threading support from Core i3 in the process. Nevertheless, we expect gamers to realize palpable gains moving from dual-core Hyper-Threaded platforms to inexpensive quad-core setups.

Core i5 and i7 also support speedier DDR4-2666 transfer rates, up from Kaby Lake's DDR4-2400 spec. Core i3 remains limited to DDR4-2400, though. This could just be Intel's attempt to segment its line-up, or perhaps the Core i3s are really just quad-core Kaby Lake designs transplanted onto a 14nm++ process. 

Unfortunately, Intel still doesn't enable Turbo Boost on its Core i3 CPUs. So, we could see a performance dip in lightly threaded workloads due to Coffee Lake's lower base frequencies. You do get 100% more cores in exchange, though. Physical cores are always preferable to logical ones, so the new implementation of Core i3 should come out ahead in most of our benchmarks.

As expected, most models continue to wield 2MB of L3 and 256KB of L2 cache per core. As a side effect of its higher core counts, then, Coffee Lake processors enjoy the benefits of more cache. Core i3-8100 is the lone exception with only 6MB of L3 cache.

PCIe connectivity remains unchanged; you get 16 lanes of third-gen PCIe from the CPU's controller. Intel reminds us, though, that it offers up to 40 lanes when we add the platform controller hub's 24.

You'll need a Z370-based motherboard for Coffee Lake processors. The 200-series chipsets are not compatible. And in a clear indication that Intel really hurried its launch schedule, less expensive B- or H-series chipsets won't be ready until next year. Paying a premium for Z-class core logic isn't much of a surprise for enthusiasts, who need the higher-end chipset to support unlocked multipliers. But it's a little bit overkill for everyone else.

We're using Intel's 1K unit pricing for comparisons to the Kaby Lake models and AMD's MSRP for price-equivalent Ryzen chips. We may see higher prices on Intel's CPUs at retail, while AMD models routinely sell below MSRP.

Intel adds a ~$20 premium to its K-series SKUs compared to their Kaby Lake equivalents. Overall, though, you pay less per core. Again, Intel removed Hyper-Threading from its Core i3s, so their price per thread remains unchanged. With the exception of Ryzen 3, AMD maintains a price advantage across its portfolio, due in part to SMT on the Ryzen 5 family. The benchmarks will give us a better idea of performance-per-dollar compared to Kaby Lake and Ryzen, though.    

Overclocking headroom was one of Kaby Lake's biggest advantages due to Ryzen's limited scaling. Intel adds per-core overclocking support to this generation, but doesn't provide per-core voltage and P-state controls. It also enables live memory timing adjustments (without rebooting), along with memory multipliers up to 8400 MT/s, so you don't have to adjust the BCLK frequency to chase bleeding-edge transfer rates. Finally, enhanced GT and Ring PLL Trim controls add more granular control.

Intel makes some power optimizations to its interface that promise to extend the advantage while overclocking. However, the company continues to insist on using thermal paste between its die and IHS, rather than solder. Like all unlocked Intel models, the Core i7-8700K doesn't include a stock cooler.

Nevertheless, we have to give the big company credit for staying on its toes this year. It already introduced Kaby Lake, Skylake-X, and Kaby Lake-Refresh. Next year, we'll have new Pentium and Celeron line-ups headed our way. But for now, we're looking forward to testing what Intel claims is its best gaming chip yet.

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