From the point of view of desktop-PC enthusiasts, upgraders, and PC gamers, the desktop versions of Intel’s 5th-Generation (“Broadwell”) Core processors arrived way later than expected—late enough, indeed, to make them only marginally relevant for those folks. The first socketed Broadwell chip, the Intel Core i7-5775C, landed in our test bed (and on store shelves) not much more than a month before we wrote this review in the first week of August 2015. We only saw the first previews of the i7-5775C at the Computex 2015 trade show in June.
With Broadwell, it was also quite an unusual time gap between the desktop and mobile parts. Desktop Broadwell, packing robust Iris Pro on-chip graphics in the i7 we tested, arrived nearly a yearafter the first 5th-Generation chips (low-power Core M ones, meant for thin laptops and 2-in-1s) were announced in September of 2014.
It seems Intel is taking a different tack with its 6th-Generation parts, which up until now have been commonly known by their code-name, “Skylake.” On August 5, 2015, in connection with the Gamescom conference in Cologne, Germany, Intel is treating PC enthusiasts and DIY PC builders to a couple of high-end socketed desktop chips early, before the mainstream 6th-Generation desktop, laptop, and mobile chips are expected to arrive, later in 2015.
Specifically, Intel is raising the curtain on what we’d expect to be its highest-end enthusiast parts on the new platform that don’t make use of the usual divergent, high-end “Extreme Edition” architecture. It announced on August 5 a four-core, four-thread Core i5-6600K processor and, the subject of our review here today, a quad-core, eight-thread-capable Core i7-6700K. Those come along with a new chipset, the Z170, that supports (among other things) both DDR3 and DDR4 memory, and more PCI Express (PCIe) lanes for multiple-video-card systems and speedy PCIe-based storage.
Rather than rattle off a full list of specs, here’s a chart detailing the two new Skylake chips, direct from Intel. Projected pricing, shown below, seems to be staying roughly the same as it was with the comparable 4th-Generation Core (“Haswell”) processors. But, as always, we’ll have to wait until the new CPUs settle into the market to be sure exactly what pricing will be.
Unsurprisingly, the arrival of substantive new features means there’s a new CPU socket involved. The new socket is called LGA 1151 (one up from the LGA 1150 of the previous generations). So, to be sure, you’ll need a new motherboard if you opt for one of these new 6th-Generation CPUs. But Intel has wisely carried over support for DDR3 RAM, along with DDR4. So, if you have an existing system and you’re looking to upgrade, you may be able to bring over your old memory if the motherboard you’re looking at supports DDR3. (A few will support both kinds; see for example the first board in our June piece from Computex Preview: Three Upcoming Skylake Motherboards From Biostar.)
That said, be sure to check the motherboard specs to make sure it supports your old RAM. The Asus Z170-Deluxe motherboard we used for our benchmark testing, for example, supports only DDR4 memory, and we expect that most enthusiast mainboards will do likewise. (We did our testing with 16GB of Corsair Vengeance DDR4 running at 2,133MHz.)
As for the Core i7-6700K processor that we’re looking at here, it’s meant to occupy the same space as last year’s Core i7-4790K (“Devil’s Canyon”) chip in the new line. And it easily surpasses that choice piece of silicon on most of our benchmark tests—specifically, on multi-core CPU-centric tests and those that can take joint advantage of both the CPU and the new HD 530 on-chip graphics. And it does so at a lower top stock clock speed of 4.2GHz. That should mean lower average temperatures overall, despite the new part’s slightly higher 91-watt thermal design power (TDP) rating.
On tasks that take advantage of just a single CPU core, though (like our old-school iTunes Conversion Test), you might not see any performance boost at all over last year’s Core i7-4790K. But at this point, unless you’re running fairly ancient legacy software, most programs that require a lot of CPU power have been coded to at least take advantage of more than one core—if not utilizing the graphics core, as well.
Skylake Basics: New Socket, New Chipsets
In an unusual move, while the Core i7-6700K and Core i5-6600K are indeed the first chips that are being released with Intel’s new 14nm “Skylake” architecture, Intel is holding off on sharing much in the way of details about that architecture for a later date. On a possibly related note, Intel’s Developer Forum, or IDF, is happening later this month, in mid-August. That would seem an ideal, well, forumfor that kind of reveal. So, for now, we’ll skip discussing the architecture details (because, frankly, we don’t know much about them) and focus instead on the new chipsets that will be supporting these initial Skylake processors.
As noted up top, you’ll need a new motherboard if you opt for the Core i7-6700K (or any 6th-Generation Core CPU), as the chips have an extra pin, and so use a socket called LGA 1151. While we’d love to see Skylake chips have backward-compatibility with older boards, those with LGA 1150-socket, Intel Z97-based boards, which came in late in the 4th-Generation Core game (with the “Devil’s Canyon” Core i7-4790K), do have the option installing a very recent 5th-Generation Broadwell CPU like the Core i7-5775C. That chip, in particular, has impressive Iris Pro graphics that, in our tests, bested the new HD 530 GPU in the Core i7-6700K, while using a much lower power/heat envelope of 65 watts, compared to 91 watts on the Core i7 Skylake chip.
That handful of Broadwell desktop chips, though, comprises the end of that particular line. If you do decide to look future-ward and opt for a 6th-Generation chip, the top-end Z170 chipset that works in concert with the LGA 1151 socket brings some fairly substantive new features. For starters, Z170 boards will support up to 20 PCIe 3.0 lanes, rather than the eight lanes of PCIe 2.0 provided by standard Z97 boards. (That is in addition to the 16 PCIe 3.0 lanes provided by the CPU, which remains the same with Skylake.) The extra lanes come thanks to an upgrade to the DMI interface that connects the CPU to the chipset, and they are important, given the rising prevalence of PCIe-based storage (via M.2, SATA Express, or drives that plug directly into a PCI Express slot, like Intel’s SSD 750 Series). Intel is also rolling out a new 800GB model of its super-fast 750 Series NVMe-equipped SSD along with these first two Skylake CPUs (a capacity we expressly asked for when reviewing that drive!), although the company hasn’t shared with us detailed pricing on that capacity of the drive yet.
Considering we’ve yet to see a graphics card saturate even eight lanes of PCIe 3.0 (which has twice the bandwidth of PCIe 2.0), you should be able to install two graphics cards in a Z170-based system, as well as up to three PCIe x4 drives, and still have six lanes to spare for other peripherals like, say, a Thunderbolt-based RAID drive box or two.
Those who need more PCIe lanes, though, will still have to step up to the pricier Intel X99 platform, and its dearly priced chips like the Core i7-5960X Extreme Edition£851.99 at Novatech Ltd. But we suspect that all but the most extreme enthusiasts and digital-content producers will be satisfied with the PCIe bandwidth offered by the Z170 chipset.
The new chipset brings support for up to three PCIe-based drives in a system, while retaining support for six SATA 6Gbps ports. For external storage, Z170 now supports up to 10 native USB 3.0 ports (up from six in Z97 boards) and 14 USB 2.0 ports. There’s no express mention of USB 3.1, either type A or C (see our primer on USB 3.1), so support for that will likely continue to depend on supplemental chips added to specific board models.
Of course, other 100-family chipsets will also be on offer with lesser features, or with features designed for business users. We saw a host of these previewed in dribs and drabs at Computex 2015, and boards based on these other chipsets (the B150, Q170, and H110, among others) should launch in the coming months, along with further details about what features they will offer. But Z170 is the highest-end chipset in the lineup, so those looking for the best features, as well as support for high-end components, shouldn’t wait for those other boards and chipsets.
We started our testing of the Core i7-6700K with our CPU-centric trials. Our comparison chips were the aforementioned Core i7-4790K “Devil’s Canyon” and Core i7-4770K (both 4th-Generation “Haswell” chips), the more recent 5th-Gen “Broadwell”-based Core i7-5775C (which has lower clock speeds but way more muscular Iris Pro graphics), AMD’s two top chips in its FX line (the FX-8370 $209.99 at Amazon and FX-9590 $239.99 at Amazon) and the AMD A10-7850K, one of its top CPU/GPU chips. For perspective, we also included the uber-powerful, eight-core Intel Core i7-5960X Extreme Edition (a $1,000 chip that, like the AMD FX processors, is a CPU only—no on-chip graphics acceleration).
Before we get into the benchmark nitty-gritty, it’s worth noting that Intel is launching the Core i7-6700K at an MSRP of $350—slightly higher than the current $340 going rate for the Core i7-4790K, but not so much higher that there’s any reason to choose the older chip, unless you happen to have an older Z97 motherboard that you’d like to stick with. And while AMD’s FX chips are power-hungrier, the FX-8370 still offers a fairly impressive amount of raw CPU performance for its $200 asking price, so long as you don’t need integrated graphics.
Also note that we tested the Core i7-6700K, as well as the other chips here, under Windows 8.1, not Windows 10. The final release build of Windows 10 rolled out just as we were wrapping up our testing of this Skylake-family chip, and we did not have time to test it (and retest the other competing processors) on the final version of the new OS. We do plan to move to testing (and perform re-testing) under Windows 10 in the near future, however.
In Cinebench R15, an industry-standard benchmark test that taxes all available cores of a processor to measure raw CPU muscle, the Core i7-6700K was left behind by the $1,000 Core i7-5960X (no surprise there) but managed a healthy-enough edge over the Core i7-4790K, and the rest of this pack…
That said, the difference between the Skylake chip and the Core i7-4790K here was far from massive, with the newer chip managing a little less than a 9 percent lead.
iTunes 10.6 Conversion Test
We then switched over to our venerable iTunes Conversion Test, using version 10.6 of iTunes. This test taxes only a single CPU core, as much legacy software does.
Music encoding doesn’t exactly push a modern CPU to its limits, and certainly not one like this. But this test still illustrates that for older programs and those that haven’t been written to take advantage of multiple cores, the Core i7-6700K may not offer any benefit over last year’s Devil’s Canyon chip. That being said, the Core i7-6700K did much better here than even the Core i7-4770K from a couple of years ago.
Windows Media Encoder
Next up was our very, very well-aged Windows Media Encoder 9 video-conversion test. We continue to use this test and report its results because, like the iTunes test, it gives a window onto performance with legacy software that isn’t fully threaded.
Here, we render a standard 3-minute-and-15-second video clip to a DVD-quality format…
Most recent high-end CPUs chew through this multi-threaded test in well under a minute. But because this is an older piece of software, it’s not fully threaded to make use of all available cores. Interestingly, and somewhat surprisingly, the Core i7-6700K notches its first win here, finishing in roughly half the time of AMD’s best FX chips, besting the “Devil’s Canyon” Core i7, the recent Broadwell Core i7-5775C, and even the $1,000 Extreme Edition CPU.
The Core i7-6700’s impressive showing here is likely down to improvements in Intel’s Quick Sync Video technology, which uses the graphics cores to speed transcoding. That makes sense, given the new chip has beefier integrated graphics than the Core i7-4790K, higher clock speeds than the Core i7-5775C, and an integrated GPU, which the Extreme Edition chip lacks.
These days, our traditional Handbrake test (run under version 0.9.8) now takes less than a minute to complete with high-end chips. (It involved the rendering of a 5-minute video, Pixar’s Dug’s Special Mission, to an iPhone-friendly format.) So, we’ve switched to a much more taxing (and time-consuming) 4K video-crunching test.
In this test, we switched to the latest revision of Handbrake (version 0.9.9) and tasked the CPUs to convert a 12-minute-and-14-second 4K .MOV file (the 4K showcase short Tears of Steel) into a 1080p MPEG-4 video…
At first, the Skylake chip stumbled on this test, finishing behind the Core i7-4790K here. But after we installed Intel’s very latest GPU drivers, the Core i7-6700K’s performance here improved greatly, and it shaved close to two minutes off the time of the Devil’s Canyon chip, for an improvement of roughly 14 percent. The Core i7-6700K also finished about 12 percent ahead of the Broadwell-based Core i7-5775C. Nice.
Next up, in our Photoshop CS6 benchmark, the Core i7-6700K looked even better, once again finishing first among other recent high-end CPUs. In this test, we run a series of 11 filters, in sequence, on a labs-standard high-res photo, timing how long it takes the system to render the effect.
While the Broadwell-based Core i7-5775C and its Iris Pro graphics did nearly as well as the new Skylake chip here, the Core i7-6700K managed to shave an impressive 20 seconds off the time of the Core i7-4790K, and it bested the Core i7-4770K’s time by 50 seconds—an improvement of about 24 percent.
POV Ray 3.7
This was the last of our CPU-centric tests. Using the “All CPUs” setting, we ran the POV Ray benchmark, which challenges all available cores to render a complex photo-realistic image using ray tracing.
Here, once again, the Core i7-6700K looked good against AMD’s FX chips, and it shaved about 13 percent off the times of the recent Intel Broadwell and Devil’s Canyon CPUs. But, as we saw in our Handbrake test, the Core i7-5960X Extreme Edition, with its ability to tackle a whopping 16 threads at once, proves the benefit of expensive high-end chips for the most-demanding CPU-centric tasks.
Early processors in Intel’s Haswell 4th-Gen desktop line did not have great reputations as overclocking candidates. As a result, Intel made a fairly big deal about its improved thermal interface (between the die and the chip-top heat spreader) with 2014’s Core i7-4790K Devil’s Canyon CPU. Even so, we (and most reviewers) achieved middling-at-best results when attempting to overclock that chip.
This time around, Intel didn’t have so much to say about overclocking potential, but the companydid make the process vastly easier (and more precise) by allowing the clock speed to be manually adjusted in the BIOS, without the limitations of multipliers or other complications. You can just dial in the frequency you’re aiming for, then save and reboot to see if it’s stable. More granular memory-overclocking adjustments are available this time around, as well, though we didn’t have time to test out those settings in detail.
Within our limited testing time, using Asus’ Z170-Deluxe motherboard, we were able to achieve a 15 percent overclock using Asus’ automatic AI Tweaker OC settings and a Thermaltake Water 2.0 Pro single-radiator cooler. After some further tweaking, we eventually got our test machine to settle, stable, at a rather impressive 4.85GHz boost-clock speed. Given more time to play around with the settings, it’s likely we could have hit even higher stable clock speeds. But of course, overclockability often varies between individual chips, so your mileage may vary. And if you don’t pay close attention to your temperatures, you can damage your processor, so be sure you know what you’re doing before aiming for high clock-speed and voltage settings.
With our 4.85GHz max clock speed, we were able to achieve a Cinebench R15 score of 1,049 (a roughly 19 percent improvement over stock speeds), and shave nearly an extra 30 seconds off of our 4K Handbrake rendering time. If our results more or less hold true for most other Core i7-6700K chips (and other overclockable “K” desktop processors in the 6th-Generation line), the Skylake may wind up being one of the more overclockable chip lines in recent memory. It also may mean Intel itself will see fit at some point to release a higher-clocked Skylake chip in the future—perhaps something like a Core i7-6890K, just as the 4790K was a “Haswell refresh” a year after the release of the Core i7-4770K.
That’s pure speculation, of course. But it does seem like the i7-6700K does have enough headroom to make a higher-clocked chip possible—especially after the Skylake manufacturing process gets refined months down the line.