The Intel Kaby Lake-X i7 7740X and i5 7640X Review: The New Single-Threaded Champion, OC to 5GHz
by Ian Cutress on July 24, 2017 8:30 AM EST- Posted in
- CPUs
- Intel
- Kaby Lake
- X299
- Basin Falls
- Kaby Lake-X
- i7-7740X
- i5-7640X
Power Consumption
With the two Kaby Lake-X processors, the main comparison for power consumption is going to be against their Kaby Lake-S counterparts on the mainstream platform. For an extra 100 MHz, Intel is moving from a 95W TDP to a 112W TDP, indicating that these processors will need better cooling – but when we tested KBL-S we were rather surprised by the power, especially on the Core i5.
The Core i5-7640X almost perfectly matches up with its Core i5 counterparts, even beating the Core i5-7600K in every situation but especially at load. For users who want to overclock near to the official TDP, it looks like there’s some headroom (other circumstances permitting). The Core i7-7740X is noticeably more power hungry at full load, hitting 79W, but lower than the Core i7-7700K at 87W.
Overclocking to 5.0 GHz
One of the elements promoted at the launch of Basin Falls was overclockability: Intel ran a private invite-only extreme overclocking workshop with sub-zero coolants that week, which was then followed by ASUS and GIGABYTE both stepping it up another gear by using liquid helium rather than liquid nitrogen. For some of these chips, the colder the better, and liquid helium is going to be limit for cooling (and cost) as there is inherent difficulty in using sub-zero coolants for records.
Those sub-zero events for records are just on single benchmarks, or single frequency records, and are not meant to be run at those speeds all day every day. This makes the air and water overclocking potential of the CPUs more important for regular users and enthusiasts.
When Kaby Lake-S was launched, we saw good overclocking performance on the Core i7-7700K: our set of 4.2 GHz base processors reached a range between 4.6 to 4.8 GHz, arguably giving a 8-15% overclock and given some of the numbers we had seen in the wild, the consistency between the processors meant that most of the 7700K CPUs could reach that amount. One of the reasons for such good performance on these CPUs was that Intel had incorporated a new feature for overclocking, the AVX offset. This allows overclockers to reduce the frequency that AVX code runs at, as this can be a limiting factor when it comes to a stable overclock. This feature is in Kaby Lake-X as well.
The end result is that the Core i7-7740X went one further in our testing, and hit 5.0 GHz all-cores at 1.25V, and completed our CPU testing suite with a -10 AVX offset. We went for 5.1 GHz all-core, up to 1.35 volts, but the temperatures were getting high and the system was still not stable. 5.0 GHz is a very respectable result, even if we only have a sample of one.
The results at 5.0 GHz are as follows. Gain is absolute for the benchmark for the 5.0 GHz value, with anything within 2.0% listed in orange. Green indicates a win for the faster chip.
| Comparison: Intel Core i7-7740X at Stock vs 5 GHz | |||
| 4.3 GHz Base 4.5 GHz Turbo Auto AVX |
5.0 GHz Base 5.0 GHz Turbo 4.0 GHz AVX |
||
| Score / Time | Web Benchmarks | Score / Time | Gain |
| 135 ms | Sunspider | 133 ms | +1.6% |
| 622 ms | Kraken | 642 ms | -3.1% |
| 45485 | Octane | 45279 | -0.5% |
| 561 | WebXPRT15 | 570 | +1.5% |
| System Tests | |||
| 2229 ms | PDF Opening | 2055 ms | +8.5% |
| 46.172 s | FCAT | 45.656 s | +1.1% |
| 1287 | 3DPM 2.1 | 1429 | +11.0% |
| 282 s | Dolphin v5 | 280 s | +0.7% |
| 891.56 s | Agisoft Total | 830.06 s | +7.4% |
| Rendering | |||
| 2474593 | Corona | 2660002 | +7.5% |
| 436 s | Blender | 485 s | -10.1% |
| 195 | Cinebench 15 ST | 215 | +10.6% |
| 986 | Cinebench 15 MT | 1084 | +10.0% |
| Encoding | |||
| 27433 | 7-zip | 29433 | +8.9% |
| 48.698 s | WinRAR | 46.633 s | +4.4% |
| 5.5 GB/s | AES | 6.2 GB/s | +12.7% |
| 25.2 FPS | Handbrake HEVC | 22.6 FPS | -10.2% |
| Office Tests | |||
| 4878 | PCMark8 Creative | 5084 | +4.2% |
| 4844 | PCMark8 Home | 5071 | +4.7% |
| 4110 | PCMark8 Work | 3984 | +3.2% |
| 19.45 per day | Chrome Compile | 17.70 per day | -9.0% |
| GTX 1080 | |||
| 72.56 FPS | 1080p Ashes Av | 76.19 FPS | +4.8% |
| 53.95 FPS | 1080p Ashes 99% | 55.45 FPS | +2.7% |
| 62.30 FPS | 4K Ashes Av | 63.46 FPS | +1.8% |
| 41.24 FPS | 4K Ashes 99% | 40.79 FPS | -1.1% |
| 103.66 FPS | 1080p RoTR-1 Av | 106.9 FPS | +3.0% |
| 85.14 FPS | 1080p RoTR-1 99% | 85.88 FPS | +0.9% |
| 61.60 FPS | 4K RoTR-1 Av | 61.33 FPS | -0.4% |
| 50.25 FPS | 4K RoTR-1 99% | 50.43 FPS | +0.3% |
There are a few obvious trends, and a couple of red flags. Most benchmarks split themselves into two groups: benchmarks with a heavy CPU component tend to get a 4-12% gain when overclocked, and those that require a lot of DRAM involvement or AVX tend to be in the 2% region. The red flags are the three big 9-10% loss values for CPU heavy benchmarks, Blender, Handbrake HEVC and Chrome Compilation.
All three benchmarks are sizable workloads with sustained high frequencies throughout, and have heavy AVX components as well. The 4.0 GHz setting for AVX could account for most of that difference, however other AVX benchmarks in our testing (Corona, Cinebench, elements of PCMark, Agisoft) do not have the same effect. The only real difference here is time: the amount of time each benchmark stays at a sustained load.
The three that had the biggest dips are our longest benchmarks: Blender at 8 minutes, Handbrake HEVC at 25 minutes, and the Chrome Compile at over an hour. In this case it seems we are hitting thermal limits for the power delivery, as explained by Igor Wallossek over at Tom's Hardware. He tested an upcoming theory that the early X299 boards are not up to the task for cooling VRMs at heavy load, and through analysis he determined that this was likely to occur in heavily overclocked scenarios. His data showed that the Skylake systems he tested, when overclocked, would hit thermal limits, come back down, and then ramp up again in a cyclical manner. He tested Skylake-X, which draws a lot more power overclocked than our KBL-X setup here, so it likely isn't affecting our setup as much, but still enough for certain benchmarks. I fully suspect we will see second-wave X299 motherboards with substantial heatsinks on the power delivery to overcome this.
More testing is needed, especially in upcoming X299 motherboard reviews. We used an early X299 prototype for our CPU testing here, and a Gaming 9 motherboard on the GPU tests (which showed little variation and no problems). We did take power numbers for this setup but when looking back on the results, they seemed off so we need to go back and re-test those.
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mapesdhs - Monday, July 24, 2017 - link
Ok, you get a billion points for knowing Commodore BASIC. 8)IanHagen - Monday, July 24, 2017 - link
Dr. Ian, I would like to apologize for my poor choice of words. Reading it again, it sounds like I accused you of something which is not the case.I'm merely puzzled by how Ryzen performs poorly using msvc compared to other compilers. To be honest, your finds are very relevant to anyone using Visual Studio. But again, I find Microsoft's VS compilar to be a bit of an oddball.
A few weeks ago I was running my own tests to determine wether my Core i5 4690K was up to my compiling tasks. Since most of my professional job sits on top of programming languages with either short compile times or no compilation needed at all, I never bothered much about it. But recently I've been using C++ more and more during my game development hobby and compile times started to bother me. What I found puzzling is that after running a few test I couldn't manage to get any gains through parallelism, even after verifying that msvc was indeed spanning all 4 threads to compile files. Than I tried disabling two cores and clocking the thing higher and... it was faster! Not by a lot, but faster still. How could it be faster with a 50% decrease in the number of active cores and consequently threads doing compile jobs? I'm fully aware that linking is single threaded, but at least a few seconds should be gained with two extra cores, at least in theory. Today I had the chance to compile the same project on a Core i7 7700HQ and it was substantially slower than my Core i5 4690K even with clocks capped to 3.2 GHz. In fact, it was 33% slower than my Core i5 at stock speeds.
Anyhow… Dr. Ian’s findings are a very good to point out to those compiling C++ using msvc that Skylake-X is probably worth it over Ryzen. For my particular case, it would appear that Kaby Lake-X with the Core i7 7740X could even be the best choice, since my project somehow only scales nicely with clocks.
I just would like to see the wording pointing out that Skylake-X isn’t a better compiling core. It’s a better compiling core using msvc at this particular workload. On the GCC side of things, Ryzen is very competitive to it and a much better value in my humble opinion.
As for the suggestion, I’d say that since Windows is a requirement trying to script something to benchmark compile times using GCC would be daunting and unrealistic. Not a lot of people are using GCC to work on the Windows side of things. If Linux could be thrown into the equation, I’d suggest a project based on CMake. That would make it somewhat easy to write a simple script to setup, create a makefile and compile the project. Unfortunately, I can not readily think of any big name projects such as Chromium that fulfill that requirement without having to meddle with eventual dependency problems as the time goes by.
Kevin G - Monday, July 24, 2017 - link
These chips edge out their LGA 1151 counter parts at stock with overclocking also carrying a slight razor edge over LGA 1151 overclocks. There are gains but ultimately these really don't seem worth it, especially in light of the fragmentation that this causes the X299 platform. Hard to place real figures on this but I'd wager that the platform confusion is going to cost Intel more than what they will gain with these chips. Intel should have kept these in the lab until they could offer something a bit more substantial.mapesdhs - Monday, July 24, 2017 - link
I wonder if it would have been at least a tad better received if they hadn't cripplied the on-die gfx, etc.DanNeely - Tuesday, July 25, 2017 - link
LGA2066 doesn't have video out pins because it was originally designed only for the bigger dies that don't include them; and even if Intel had some 'spare' pins it could use adding video out would only make already expensive mobos with a wide set of features that vary based on the CPU model even more expensive and more confusing. Unless they add a GPU to either future CPUs in the family (or IMO a bit more likely) a very basic one to a chipset variant (to remove the crappy one some server boards add for KVM support) keeping the IGP fully off in mainstream dies on the platform is the right call IMO.DrKlahn - Monday, July 24, 2017 - link
Great article, but the conclusion feels off:"The benefits in the benchmarks are clear against the nearest competition: these are the fastest CPUs to open a complex PDF, at the top for office work, and at the top for most web interactions by a noticeable amount."
In most cases you're talking about a second or less between the Intel and AMD systems. That will not be noticeable to the average office worker. You're much more likely to run into scenarios where the extra cores or threads will make an impact. I know in my own user base shaving a couple of seconds off opening a large PDF will pale in comparison to running complex reports with 2 (4 threads) extra cores for less money. I have nothing against Intel, but I struggle to see anything in here that makes their product worth the premium for an Office environment. The conclusion seems a stretch to me.
mapesdhs - Monday, July 24, 2017 - link
Indeed, and for those dealing with office work it makes more sense to emphasise investment where it makes the biggest difference to productivity, which for PCs is having an SSD (ie. don't buy a cheap grunge box for office work), but more generally dear god just make sure employees have a damn good chair to sit on and a decent IPS display that'll be kind to their eyes. Plus/minus 1s opening a PDF is a nothingburger compared to good ergonomics for office productivity.DrKlahn - Tuesday, July 25, 2017 - link
Yeah an SSD is by far the best bang for the buck. From a CPU standpoint there are more use cases for Ryzen 1600 than there is the i5/i7 options we have from HP/Dell. Even the Ryzen 1500 series would probably be sufficient and allow even more per unit savings to put into other areas that would benefit folks more.JimmiG - Monday, July 24, 2017 - link
The 7740X runs at a just over 2% higher clock speed than the 7700X. It can overclock maybe 4% higher than the 7700X. You'd really have to be a special kind of stupid to pay hundreds more for an X299 mobo just for those gains that are nearly within the margin of error.It doesn't make sense as a "stepping stone" onto HEDT either, because you're much better off simply buying a real HEDT right away. You'll pay a lot more in total if you first get the 7740X and then the 7820X for example.
mapesdhs - Monday, July 24, 2017 - link
Intel seems to think there's a market for people who buy a HEDT platform but can't afford a relevant CPU, but would upgrade later. Highly unlikely such a market exists. By the time such a theoretical user would be in a position to upgrade, more than likely they'd want a better platform anyway, given how fast the tech is changing.