Skylake: Intel's Core i7-6700K And i5-6600K

Overclocking

The overclocking community isn’t always happy with the decisions that Intel makes in pursuit of greater integration, improved efficiency or even just lower cost. We’ve seen lower-quality thermal interface material, restrictive ratios and integrated voltage regulation affect tuning in different ways. Overall, though, the company seems receptive to feedback from the enthusiasts pushing its products beyond their factory specifications.

Sometimes the alterations are superficial in nature. Devil’s Canyon saw Intel make adjustments to the Haswell architecture’s power delivery and thermal performance. But we were still stuck with BCLK ratios, around which the base clock could only be manipulated plus or minus a few megahertz. A new architecture like Skylake gives Intel the opportunity to reevaluate more fundamental subsystems and change their behavior. With that in mind, the Core i7-6700K and Core i5-6600K represent a significant step forward in many ways, even if certain details remain unavailable (for example, what’s Intel using between its die and heat spreader this time?).  

To begin, the Platform Controller Hub’s reference clock to the PCIe bus and I/O is fixed at 100MHz. A separate BCLK signal from the PCH facilitates tuning the processor’s cores, cache, graphics subsystem, memory controller and system agent in 1MHz increments up to 200MHz.

That signal is multiplied against a number of different ratios to dial in optimized clock rates. The cores, for instance, support ratios of up to 83x—higher than Haswell’s 80x ceiling, but far beyond the CPU’s practical limit in both cases. As with Haswell, Skylake’s ring bus ratios are not locked to the cores. Adjustments are available up to 83x as well, though you can detune the ring if you suspect it of holding back a more aggressive overclock elsewhere. The graphics engine offers ratios up to 60x, similar to Haswell and Ivy Bridge. And if you have a mobile Skylake CPU with embedded DRAM, adjustable ratios facilitate a first opportunity to improve its performance through overclocking.

Intel’s early overclocking documentation suggested that memory ratios would be available up to 24x (at 133MHz) and 31x (at 100MHz), creating a maximum of around 3200 MT/s. However, the company's launch material mentions data rates of up to 4133 MT/s. We have kits in-house capable of 3600 MT/s, so there’s still room to scale up as motherboard vendors continue optimizing. Whereas previous architectures exposed ratios that stepped memory data rates up and down in 200/266 MT/s increments, Skylake is more granular with 100/133 MHz steps. The addition of XMP 2.0 simply accounts for a new DDR4 specification. Intel’s XMP certification process remains unchanged, though.

Gone is the fully-integrated voltage regulator, which many enthusiasts faulted for making their Haswell-based CPUs run hotter and require higher-end cooling. It remains to be seen how much impact this has on real-world results, particularly since we’re dealing with a completely different architecture.

Our Hands-On Experience

It’s early in Skylake’s life, and we’re still testing pre-production samples. We weren’t particularly optimistic about the architecture’s scalability given Intel’s 4GHz base clock rate and 4.2GHz peak Turbo Boost frequency on the Core i7-6700K. However, our experience so far suggests that 4.7GHz could be a reasonable target with minimal voltage increase.

One of our samples even cruised along at 4.9GHz using a 1.41V setting, but it wasn’t stable under load, and we’re not comfortable with that voltage.

We didn’t go to the trouble of trying to find our i7-6700K’s breaking point using single-megahertz BCLK adjustments. But just to show Intel’s more flexible BCLK controls do work, we set the reference clock to 115MHz and snapped the following screen shot:

We also devoted more time to testing DDR4 memory scaling. Corsair and G.Skill both sent in kits capable of 3200 MT/s. Additionally, Corsair followed up with a 3600 MT/s configuration. Using MSI’s Z170A Gaming M7 motherboard, we tested at 2133, 2400, 2666, 2933 and 3200 MT/s. Both companies’ kits were rock solid using MSI’s default 3200 MT/s settings and their XMP profiles. But we weren’t able to get 3600 MT/s dialed in; Windows consistently crashed as it started up.

In the hours before launch, MSI did send over a firmware update that got 3466 MT/s stable, albeit at lower bandwidth than 3200 MT/s. It's only a matter of time, though, until even more aggressive memory settings become viable. Intel's early overclocking guidance suggested that ratios enabling 3200 MT/s would be possible and now the company is throwing around numbers like 4133 MT/s. Motherboard vendors are quickly optimizing for the enthusiast-oriented memory kits popping up in anticipation of Skylake, so expect more on this front soon.

Bandwidth continues to scale with data rate. Starting at 2133 MT/s, a >23 GB/s result certainly isn’t bad for a dual-channel controller. By the time you get to 3200 MT/s, though, you’re up above 32 GB/s—an almost-40% increase.

Of course, real-world performance doesn’t improve nearly as much. Intel’s desktop configurations typically aren’t starved for data given the workloads we hit them with, so a best-case speed-up in WinRAR is more like 6-7%. And that’s a test we know to be at least somewhat sensitive to memory performance. Pretty much everything else we run is less responsive.

Interestingly, it’s not at the highest data rate where performance is best, either. DDR4-2933 appears to be the peak, after which bandwidth keeps going up while our timed benchmarks slide ever so slightly.

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  • rantoc
    Yawn... its easy to see that intel have to little competition, they have stagnated in the cpu performance department!
  • daniel266
    Can we have comparisons of rendering software using win 8.1 and win 10 ??
  • cats_Paw
    Still 4 cores.... Im sticking to my Q6600.
  • Vlad Rose
    What the heck Intel? So, you provide great integrated graphics into Broadwell, then nerf it for Skylake? I guess you had to find a way to help sell your 'paper launch' of Broadwell. I really hope Xen makes you guys wake up; although it more than likely won't.
  • Bartendalot
    At least Skylake HEDT should be powerful. Unless DX12 pulls a rabbit out of a hat, this doesn't look promising for anyone who has Sandy or higher.
  • stairmand
    Quote:
    Still 4 cores.... Im sticking to my Q6600.


    Then you really are missing out, 4 cores or not a current i5 (let alone an i7) will simply destroy the old Q6600 C2Q. It was great in the day but it's very old hat now and the lack of features on the board worse still.
  • salgado18
    Quote:
    Still 4 cores.... Im sticking to my Q6600.

    You do know that your Q6600 is astronomically slower than Skylake in every single department, right? By your logic, the Phenom II X6 is better than the i7 6700K.

    I think you should consider upgrading. You won't regret, promise.
  • salgado18
    Quote:
    What the heck Intel? So, you provide great integrated graphics into Broadwell, then nerf it for Skylake? I guess you had to find a way to help sell your 'paper launch' of Broadwell. I really hope Xen makes you guys wake up; although it more than likely won't.

    Do you mean Shen, from LoL? Or Zen? XD

    I believe the cost of the integrated memory chips would make these processors too expensive and niche to be viable products.
  • Lmah
    Good upgrade for 1st Gen i5/i7 users. Though I think they targeted it at the 2nd Gen i5/i7 users, doesn't seem like a huge improvement for them though.
  • vertexx
    Why no discrete graphics tests?
  • Cryio
    Skylake, the 1st worthy upgrade for Sandy Bridge users. If average IPC improvements from Sandy to Broadwell are ~13%, Skylake should make this difference even higher. Lower power usage, same OC ability or higher and we have a winner.
  • Vlad Rose
    120171 said:
    Quote:
    What the heck Intel? So, you provide great integrated graphics into Broadwell, then nerf it for Skylake? I guess you had to find a way to help sell your 'paper launch' of Broadwell. I really hope Xen makes you guys wake up; although it more than likely won't.
    Do you mean Shen, from LoL? Or Zen? XD I believe the cost of the integrated memory chips would make these processors too expensive and niche to be viable products.


    Xen- AMD's next generation CPU.
  • logainofhades
    1629708 said:
    Xen- AMD's next generation CPU.


    It is Zen, not Xen.

    I am not all that impressed, really. I see no real reason to upgrade from my 3570k. Taking a step backwards, on the IGP, makes 0 sense, also.
  • Yuka
    Quote:
    1629708 said:
    Xen- AMD's next generation CPU.
    It is Zen, not Xen. I am not all that impressed, really. I see no real reason to upgrade from my 3570k. Taking a step backwards, on the IGP, makes 0 sense, also.


    I disagree completely in the iGPU part. You don't need every generation of mainstream CPUs to have performance improvements so massive in terms of iGPU. Intel still has a lot of work to do driver wise and pulling better and better hardware doesn't put them in a better position.

    Plus, a better iGPU means less actual CPU. If you ask me, I think this OC is possible because they held back on iGPU and process maturity helped a lot.

    Cheers!
  • karab
    Quote:
    Still 4 cores.... Im sticking to my Q6600.


    This is a good joke. You are a funny person.
  • ubercake
    Quote:
    1629708 said:
    Xen- AMD's next generation CPU.
    It is Zen, not Xen. I am not all that impressed, really. I see no real reason to upgrade from my 3570k. Taking a step backwards, on the IGP, makes 0 sense, also.


    I know. I keep waiting for a reason to upgrade my 3930K setup and this is yet another gen I won't bother with. I thought they'd at least start giving us 6 cores standard with this gen. Not so.
  • Math Geek
    i like the pricing for the chips which is basically the same as current 5th gen i5/i7. too bad the new mobo and ddr4 ram will drive the total cost way skyward in the beginning. can't wait for those prices to drop and match current ddr3 and z97 mobo's. then we're talking a bit better.

    and why the hate on the igp? the AMD apu's have had a solid igp for a long time now yet all they get is hate since "no gamer uses an igp anyway" so now intel gets the igp hate as if folks will use it? so gamer will use the intel igp but not the amd one? come on folks can we at least be marginally consistent with the hate?? do gamers/enthusiasts care about igp or not?

    i'm more confused than a hungry baby in a strip club!!
  • royalcrown
    I do like the platform upgrades, specifically thunderbolt and new USB speeds. We just need more stuff that would use them. As far as the CPU, not so excited, like most of you.

    How many would upgrade if there was lots of thunderbolt and USB peripherals, and they weren't stupidly expensive ?
  • xenol
    I'm not bummed about the IGPU taken a step back because for the most part, most people who buy one of these aren't going to use it anyway. Unless Intel and others have finally implemented desktop switchable graphics.
  • wtfxxxgp
    I don't understand the negativity. It's brand new. Even the mobos and memory will be fresh and new. I honestly think that Intel still has a sucker-punch waiting to be revealed depending on what Zen is capable of. Why bring out your very best when mediocre is enough to beat your closest competitor, after all? It's far more lucrative to keep providing small incremental updates and charge a premium for every iteration than it is to say wham-bam and provide the masses with your very best effort and then have to charge a massive premium for it. I say be happy, every new bit of tech comes with advantages. I AM disappointed about the IGP though. These days I find myself playing MOBA games that don't require a lot of muscle - I'd love it if I could get a brilliant CPU and more than adequate IGP without having to shell out more money for a discrete GPU. I hope they do release something more top tier in both areas on the same CPU - I'll definitely purchase something like that.
  • royalcrown
    Something like when Thomas Edison said, "Never give them the best first." I think it was him anyhow.

    I agree from a business perspective, but from the perspective of actually advancing our computing paradigms and platforms, it is holding things back. The "speedbump" junk is a ball and chain on the ankle of advanced tech. It's screwing US a lot.

    976586 said:
    I don't understand the negativity. It's brand new. Even the mobos and memory will be fresh and new. I honestly think that Intel still has a sucker-punch waiting to be revealed depending on what Zen is capable of. Why bring out your very best when mediocre is enough to beat your closest competitor, after all? It's far more lucrative to keep providing small incremental updates and charge a premium for every iteration than it is to say wham-bam and provide the masses with your very best effort and then have to charge a massive premium for it. I say be happy, every new bit of tech comes with advantages. I AM disappointed about the IGP though. These days I find myself playing MOBA games that don't require a lot of muscle - I'd love it if I could get a brilliant CPU and more than adequate IGP without having to shell out more money for a discrete GPU. I hope they do release something more top tier in both areas on the same CPU - I'll definitely purchase something like that.
  • bystander
    What tests are you looking at, the IGP is faster than previous models, unless you look at the Iris and Iris Pro comparisons, which are specialty parts. Skylake will likely get an Iris and Iris Pro version as well.
  • legion_of_cheese
    Quote:
    Quote:
    Still 4 cores.... Im sticking to my Q6600.
    You do know that your Q6600 is astronomically slower than Skylake in every single department, right? By your logic, the Phenom II X6 is better than the i7 6700K. I think you should consider upgrading. You won't regret, promise.

    Quote:
    Quote:
    Still 4 cores.... Im sticking to my Q6600.
    You do know that your Q6600 is astronomically slower than Skylake in every single department, right? By your logic, the Phenom II X6 is better than the i7 6700K. I think you should consider upgrading. You won't regret, promise.

    Quote:
    Quote:
    Still 4 cores.... Im sticking to my Q6600.
    Then you really are missing out, 4 cores or not a current i5 (let alone an i7) will simply destroy the old Q6600 C2Q. It was great in the day but it's very old hat now and the lack of features on the board worse still.

    Quote:
    Quote:
    Still 4 cores.... Im sticking to my Q6600.
    You do know that your Q6600 is astronomically slower than Skylake in every single department, right? By your logic, the Phenom II X6 is better than the i7 6700K. I think you should consider upgrading. You won't regret, promise.


    In which way is he saying that the CPU he has is better/superior? He simply doesn't. Having less features or speed doesn't mean nothing when the user is comfortable with the performance. I have a friend who still has i7 970 and is still satisfied by it.

    You guys easily get mad at such statements which are ambiguous. Stop faning too hard.
  • InvalidError
    1786133 said:
    and why the hate on the igp?

    The rationale most enthusiasts use is that the die area used by the IGP could have been used for more cores or more cache, or that the die area could have been reduced to lower cost.

    As for why they are more upset about AMD focusing on CPUs with IGPs, that would likely have to do with how AMD lags so far behind Intel on CPU performance under most scenarios. Since the gap between AMD and Intel CPU performance is so wide, people simply accept Intel's IGP as part of the price premium. For those who adamantly refuse to pay for an Intel IGP of any sort, even disabled as is the case with some LGA115x Xeons, but still want Intel's CPU performance, there are the LGA2011(-v3) options.