Intel Core i9-7900X X-Series Skylake-X CPU Review

Introduction, Specifications, and Pricing

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Competition between vendors doesn't happen in real-time these days. Instead, it happens in a series of strategic product launches. While Skylake-X and Kaby Lake-X (I will refer to them as Sky-X and Kaby-X from here on out) were both on the books since before Ryzen launch, it does seem that Intel has strategically priced these new processors based on their performance in response to the competition.

Skylake-X brings about more than just multiple Skylake-S cores put together; it also offers cache changes, a shift to an integrated VRM, the additional of AVX-512, and the use of a 2D mesh interconnect instead of a ring bus.

Let's see how the current top dog i9-7900X does.

Specifications

As many people know, since we already wrote about the specifications of the CPU, the i9-7900X features 10 cores and 20 threads, a 140W TDP, and 13.75MB of restacked L2 cache. Intel cut L3 cache density in half while quadrupling the L2 cache. You can read about that here.

Intel is also introducing Turbo Boost 3.0 again, but this time, support for it should be native to Windows 10, so you won't need a driver. Turbo Boost 2.0 allows for two cores to go to 4.3GHz, two to go to 4.1GHz, and the rest to hit 4.0GHz. Turbo Boost Max 3.0 is additional to Turbo Boost 2.0. The CPU also offers support for 128GB of memory, and a higher memory speed of 2666MHz.

Pricing

The Core i9-7900X should be priced around $1000.

The CPU and New Additions

The CPU

The top of the CPU features a very large heat spreader like the one Broadwell-E used. The bottom is where we find the pads that fit into the LGA2066 socket. The new socket's mounting hardware allows for the use of LGA-2011 heat sink coolers; we are glad Intel decided not to change the cooler mounting.

To Skylake-X does have a chip on it labeled "642 X8", and it is a RFID tag. However, Intel confirms that is does nothing on consumer SKUs; it's just a holdover from the fact that Skylake-X CPUs are from the top of the stack, meaning they are lower-end equivalents of their Xeon counterparts.

New Additions

Skylake-X uses the Skylake microarchitecture, which is pretty much the same as the Kaby Lake architecture. However, while Kaby Lake-X is basically a transplant of its Z270 counterpart, Skylake-X is not. It has a few changes, but the core microarchitecture remains the same.

It has an improved front-end and increased bandwidth, but we have known this since Skylake launched over a year ago, so the slides above are just a rehash of the changes made in Skylake over Haswell. At the time, Intel called it their "Best CPU Ever," and it did provide roughly 7% IPC increase over Haswell.

Intel rebalanced the cache hierarchy, and now the L3 cache, which is half the size it was in the previous generation, acts as a victim cache and is filled with evictions from the L2 cache (which is private to each core). The L2 cache is quadruple the size it was in previous generations, bringing cache closer to each core. Intel has also shifted to a mesh architecture from a ring.

CPU interconnect layout is very important, and it can also account for anywhere from 15-30% of the CPU's power budget. The reason for this shift was not only to facilitate better interconnects for higher core count CPUs but also perhaps because of this change in cache policy and distribution.

AVX512 has also been added to Skylake-X, and the new library offers many different optimizations along with some very useful instructions that can be easily taken advantage of to improve performance. The types of optimizations are especially useful in workstation and above applications, which is one of the targets of the Skylake-X line of processors.

Test Setup and New Hardware

Test Setup

Since many of you asked, I have upgraded my GPU from the GTX 980 to a GTX 1080 Ti. I have three motherboards on hand and one new memory kit. The motherboards were all used; one for overclocking, one for out of the box performance, and one for Intel optimized performance (correct specified with Turbo 3 and 2666MHz memory).

However, for this review, I used two memory kits (one Corsair and one G.Skill). The Dominator Platinum Kit I used isn't new to my reviews, just a 32GB 4x8GB dual rank kit rated to 3200MHz, the G.Skill is so I will picture it below.

• CPU: Intel Core i9-7900X
• Motherboard: One of The Three Below
• Cooler: Corsair H100i V2 AIO Water Cooler
• Memory: Corsair Dominator Platinum 32GB and G.Skill TridentZ RGB 32GB
• Video Card: NVIDIA GeForce GTX 1080 Ti - Buy from Amazon / Read our review
• Storage - Boot Drive: Samsung 950 Pro 256GB M.2
• Storage - USB Drive: Corsair Voyager GS 64GB - Buy from Amazon / Read our review
• Case: Corsair Obsidian 900D - Buy from Amazon / Read our review
• Power Supply: Corsair RM1000 - Buy from Amazon / Read our review
• OS: Microsoft Windows 10 - Buy from Amazon
• Monitor: ASUS PA328 ProArt 32" 4K - Buy from Amazon
• Keyboard: Corsair K70 LUX - Buy from Amazon
• Mouse: Corsair M65 PRO RGB - Buy from Amazon / Read our review
• Headset: Corsair VOID RGB Wireless - Buy from Amazon / Read our review

New Motherboards and RAM

We have added a beautiful Trident Z 4x8GB RGB LED memory kit to our review test bench for X299.

I am ordering the motherboards in the order I received them. While I picked up a GIGABYTE X299 Aorus Gaming 9 at a workshop for Skylake-X, GIGABYTE also sent over their Gaming 7. They have a lot of RGB inside of them.

The motherboards feature multiple M.2 slots, and they have actual heat sinks that will hold those pesky M.2 screws in place. The IO panel of the Gaming 9 (the one used in this review for overclocking) features an equal amount of USB 3.1 type-A to USB 3.0 type-C, but that has to come from controllers since the X299 PCH doesn't offer integrated USB 3.1.

I also wanted to highlight one more thing; notice those oddly shaped rectangles below the first M.2 shield? Those are a new type of PCI-E switch, and they had to be used to facilitate Kaby-X and Skylake-X PCI-E switching. The PCI-E layouts on X299 motherboards can be extremely confusing, as it's very hard to support 16, 28, and 44 lane CPUs all on the same motherboard, so new switches that could switch in more than two directions or take more than one input had to be used.

The RGB memory and the motherboard's built-in RGB LEDs look really cool, and I am serious. It's a little in your face, but if you are going to go all in with an RGB motherboard, this is definitely the one that screams RGB.

MSI sent us an X299 Gaming Pro Carbon/AC, which offers the ability to change the heat sink panels to ones with different colors or designs. They even sent us customized "TweakTown" designed panels.

MSI is also offering a high amount of USB 3.1 and USB 3.0 on their motherboard, as well as Intel wireless-AC. The motherboard features two M.2 shields, these shields act as heat sinks and are a bit improved compared to the MSI Z270 counterparts. Here we can also see a lot more quick switches than we did on X99 motherboards, and that is because of the support for Kaby-X.

MSI doesn't fail us, they also have RGB LEDs, and here we can see "TweakTown" written on the VRM heat sink panel. The RGBs are a little less pronounced, so they produce a laid back ambiance.

ASUS sent over their PRIME X299 Deluxe, which offers a nice white and black aesthetic design.

ASUS also offers M.2 heat sinks, but more interestingly Wireless AD along with a plethora of USB 3.1, 3.0, and 2.0 ports. The motherboard is loaded with features.

ASUS went a different and more classic route with RGB LEDs, offering a few lit panels, and an LCD screen at the center of the motherboard that shows some cool stats, I liked it when the system was booting because I could see what was going on if the system was hanging. It actually spells out what the POST Code errors are.

Out of the Box Performance: CINEBENCH, wPrime, and AIDA64

Remember: "7900X" refers to a 7900X running under Turbo Boost 2.0 and JEDEC memory speeds of 2133MHz (no optimization, and below spec.) and "7900X Intel Optimized" refers to a 7900X running using Turbo Boost Max 3.0 and DDR4 2666MHz memory.

Intel Optimized is according to Intel spec and not considered overclocking; it's what you will score near out of the box, the other results are from earlier BIOS versions. I put in the work, so I guess you can think of them as Turbo Boost 2.0 scores at JEDEC memory speeds.

The 7900X, in either case, is a workstation/content creation beast and a worthy opponent for any 10-core processor and in CINEBENCH is roughly 15% faster in multithreaded even un-optimized, and more than 20% faster in single core performance. However, that single Skylake-X core is running at a faster top speed.

The processor is also significantly faster in W-Prime, and the AIDA64 results might be bugged since the program warned that it hadn't been optimized, but that difference is huge! Perhaps due to the mesh and L2 cache changes. Un-optimized, memory speeds are not as fast as the 6950X, but when we optimize they are.

Out of the Box Perf.: Handbrake, ScienceMark, and SuperPI

Handbrake shows significant improvements in both 4K and 1080P video transcoding. Science Mark shows us something interesting, or at least the beginnings of something interesting. Intel has definitely boosted Skylake-X performance by implementing a mesh interconnect architecture and re-configuring cache, and while that's all great, it doesn't mean there won't be any performance pitfalls.

Engineering is about trade-offs, and that is what we see here. Skylake uArch is quite fast in single-threaded, and it shows in SuperPI.

Out of the Box Synthetic Gaming Perf.: UNIGINE and 3DMark

FireStrike and CloudGate benchmarks show us where the frequency and memory boosts help Skylake-X over Broadwell-E. Without Turbo Boost 3 (the memory isn't that important in these benchmarks), Broadwell-E might have the upper hand. However, Intel is targeting content creators more so with the platform, and soon enough Turbo Boost Max 3.0 will work without any effort on all motherboards, probably by the time you can buy the product in stores.

Unigine seems to like the 7900K, but it likes the 7700K better.

Out of the Box Gaming Performance

It's clear, with Turbo Boost Max 3.0, Skylake-X is Intel's best gaming CPU other than the 7700K in our charts (I don't know how the other Skylake-X or Kaby Lake-X CPUs perform yet), but without it, we see it tie or perhaps lose to the 6950X. The good news is that it costs $700 less than the 6950X. I should mention that Intel Optimized just means Intel Stock.

The issue is that the normal 7900K results were done on older BIOS versions, while the new ones are done on the latest BIOS versions that support Turbo 3 without any software requirements. You will see results in line with the better performing 7900X results, but I do know some other media who were getting the same low gaming scores I was, and that was because Turbo 3 wasn't working.

Memory increase from 2133Mhz to 2666Mhz with the same timings also makes a difference in the gaming results. Ashes of Singularity is one of our outliers, but that is most likely because they have to optimize the code for the CPU, just like had to be done for Ryzen.

Overclocking and Power Consumption

CPU Overclocking

I was able to get a nice 4.6GHz on all cores, but of course, you might do better. I would say almost all CPUs can do 4.5GHz on all cores, and even then, the CPU is a monster. I just ran quick CINEBENCH runs; I will do more overclocking investigation when I have more time, as I have only had the sample for a few weeks and had to re-run tests with every new BIOS (more times than I can count).

Overclocking memory on this platform is very easy, the IMC is very well tuned, and it seems that 3200MHz isn't the maximum any longer. Many motherboard vendors have been touting memory speeds over 4GHz, so we should see 3600MHz+ become the standard soon.

CPU core overclocking is a bit trickier because of the massive amounts of heat. A Corsair H100i will let you pump only around 1.25-1.27v before you thermal throttle, so better cooling helps. Even so, I was able to get to 4.6GHz without thermal throttling but to be honest; sometimes it doesn't hurt performance that much as you will see below. I would try and keep temperatures below 80C, but I guess with this processor we are aiming for 90C.

By decreasing the input voltage, I was able to shave a few degrees off one of the cores, so that only three had any type of thermal even at 4.7GHz. The reason that decreasing the ratio between the VCore and input voltage lowers temperatures is because it helps the efficiency of the input VR. Although there are thermal events in both of these scores, they are both higher (although the one with three events rather than four scores better) than the 4.6GHz score.

I believe that on this platform, it will be easier to scale the cores and peg a few high and the rest lower in a step-wise fashion.

Power Consumption

Our numbers were quite shocking to be honest, especially since the CPU isn't overclocked. They say that CPU interconnects take up about 15-30% of the power budget, and it seems that the mesh did add some power consumption.

We also have an integrated VRM and higher clocks to contend with. The integrated VRM lowers the efficiency of the power conversion, so instead of it all being external of the CPU and on the motherboard, it is now shared in two different stages, putting less strain on each stage but decreasing overall power conversion efficiency.

Our results of the CPU power consumption are measured at the 8-pin power connectors, and in this case both, so we went through both levels, and actual power consumption for TDP ratings is obviously going to be a bit lower.

What's Hot, What's Not & Final Thoughts

This is where you can fast forward to the final section of the review, and get a quick recap and points on the Core i9-7900X.

What's Hot

Cache, Mesh, and IVR: Intel knows how to build huge CPUs, it's basically a huge chunk of their business, and they have become pros at it. When news of the mesh hit, I went back and did some research, and it turns out that Intel had been doing its research for over a decade into the most efficient CPU interconnect technologies for HCC (high core count) processors. Obviously, it and the change to cache allocation have paid off, as we are getting more regarding overall multi-core performance than we expected.

Big Multi and Single Core Performance Jump: Skylake-X has done better than I expected regarding raw performance. Intel also went to great lengths to increase multi-core performance through cache reallocation and the mesh, but that took a hit on single core performance. To remedy this hit, Intel used its secret weapon - its 14nm process. Skylake-X can overclock all cores to 4.5GHz, and with ease, but further than that you are battling heat, not the capability of the cores. Out of their high clocking 14nm process Turbo Boost Max 3.0 is born, and now native to the OS, you don't need a driver.

Price: Some of you might not agree with me on this, as you can get 8-Ryzen cores for less than half this price, but you can now get the latest 10C/20T Intel CPU for $700 less than you could yesterday. Compared to itself, there is an apparent price drop that Intel probably wouldn't have provided if Ryzen didn't do what it did - competition helped us all!

Memory Overclocking and All Cores 4.5GHz: While 4.5GHz is what most 7900X will be able to do without much effort (you might need to manual set VCore to 1.25v, so the CPU doesn't go wild with itself), you can take memory upwards of 4GHz with ease. While that might not sound so impressive, what is impressive is that out of the gate, motherboard vendors have support for memory faster than 4GHz at launch, and that is impressive.

What's Not

Power and Heat: The 7900X is best for cold regions, where you might as well get your bang for the buck and game for free instead of running your central heater - energy is never destroyed, just transformed. All joking aside, high performance does result in high power consumption, and the 7900X is not an exception. The IVR (integrated voltage regulator), the mesh, and the higher core frequency all have some disadvantages: heat is one of them.

TIM: I am not sure why Intel didn't use solder, as they almost always do since the larger die size allows for it on their X99 CPUs, but the TIM isn't helping thermals when overclocking. De-lid tools are going to be in demand.

Final Thoughts

Intel did a great job addressing the market of content creators who figured out that Ryzen was basically a steal at its price point. It had the same multi-threaded performance as the 6900K, but for half the price.

Intel has addressed that by adding two more cores, increasing multi-core performance, and even increasing single core performance. Without Turbo Boost Max 3 and its boost to the 7900X's single core performance, we could have come to a different conclusion. However, since the technology will be native and not require a driver, we can applaud Intel for thinking about all aspects of the processor.

However, the road here was a rocky one, and many of us in the media had to retest the Skylake-X CPUs last minute to see the effects of the Turbo Boost Max 3. Since that road was rocky, we also saw vendors invent their own Turbo profiles, most of which throttled the CPU, but now that most vendors seem to have things under control, the public will probably not see the BIOS versions of weeks past. I also want to mention AVX512, as it shows Intel's commitment to increasing compute power in their latest CPUs.

They increased peak FLOPs eight times over four generations, and that can't be ignored. Whatever made Intel drop the price of their 10-core part, also made the 7900X an attractive CPU for those with the budget.

If anything, we know Intel won't just sit around and play the game as it has done for the past few years, and the 7900X is evidence of that.