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Skylake-X and Kaby Lake X: The Core Wars Skylake-X and Kaby Lake X: The Core Wars
Intel hits back with new CPUs and a matching chipset. We examine the state of play in the latest round of the CPU wars.... Skylake-X and Kaby Lake X: The Core Wars


Intel hits back with new CPUs and a matching chipset. We examine the state of play in the latest round of the CPU wars.

Intel’s response to AMD’s Ryzen 7 ten-core CPU came faster than anybody could have imagined. At this year’s Computex, the company announced the new Core-X series of processors, based on the Skylake-X and Kaby-Lake X architectures. Now, Intel had originally planned to release Skylake-X at the end of this year, or even early 2018, so rushing it forwards by six months means it likely hasn’t undergone the rigorous testing that Intel usually does, as we’ll discuss soon. However, it does mean that it has a range of new products that compete with the Ryzen processor, though purely on performance, not price. It’s a rather odd launch, with Skylake-X being a relatively major upgrade to Intel’s design, while Kaby-Lake X isn’t. Let’s see what’s the deal with Skylake-X first.

Skylake-X for the best

There will be nine new CPUs in the Core-X family, but currently only five have launched. The top seven CPUs are all based on the Skylake-X design, while the bottom two use Kaby-Lake X. The fastest chip currently available is the ten-cored, 20-threaded i9-7900X, which currently retails for around $1,440. That’s still double the price of AMD’s ten-cored, 20-threaded Ryzen 7 1800X, so it had better run rings around AMD to justify the price hike. 

The i9-7900X is built on the same 14nm enhanced process of Intel’s previous generation of CPUs, but the company won’t supply info on how many transistors it has. Eventually we’ll see the release i9-7980XE, which will have a whopping 18 cores, but until now the i9-7900X is the top of the line. It has a base frequency of 3.3GHz, but can Turbo up to 4.3GHz. Just like AMD, Intel has incorporated a second level of Turbo called Turbo Boost Max 3.0, which theoretically brings the CPU speed up to 4.5GHz if the thermal conditions are right. We say theoretically, as it didn’t work on three of the four motherboards we tested – every time we tried to install the necessary drivers, we’d encounter an error saying “ITBM Driver not Available Existing Application”. 

As a result, all of our boards – bar the MSI X299 Gaming Pro Carbon AC – were limited to 4.3GHz, even when we tried to overclock them using their automatic overclocking features. Only the MSI board worked correctly, hitting 4.5GHz during our testing. There’s obviously some work to be done on the driver and BIOS support for this feature. 

With ten cores, this chip is a bit of a power-hog, with a max TDP of 140W and an operating voltage around 1.7V. You’ll need to bring your own cooling too; we used the Corsair H105. The i9-7900X brings plenty of PCIe 3.0 lanes to the table, with a maximum of 44. However, as you progress down the stack, the number of lanes drops, to 28 on the i7-7820X and then 16 on the I7-7740X. 

Skylake X has had some rather significant changes to its designs. For starters, Intel has ditched the Ring topology it used to connect the cores in the past, and now uses what it calls a ‘mesh interconnect’ technology. Apparently, this allows for lower latency between each core, as well as higher bandwidth between each core. 

Intel has also shifted the caches around. Now each core gets a full 1MB of L2 cache, up from 256kB on the previous high-end CPUs. The bandwidth between the L1 and L2 caches has been increased to 128 bytes per cycle, which Intel claims quadruples the associativity between the cache from four to 16. Not all caches have been increased though, with Intel dropping the last level of cache from 2.5MB per core down to 1.375MB. 

Kaby-Lake X for the rest

The other CPU sent to us was the i7-7740X, which uses the Kaby-Lake X design. This is a far less interesting CPU, as it’s basically identical to the i7-7700 with the exception of the new form factor, yet costs $30 more at $500. All of the new Core-X CPUs have 2066 pins, to fit into the new LGA 2066 socket on the accompanying X299 chipset that Core-X must be used for. Unfortunately the new pin count, which is 55 higher than the last generation, means you won’t be able to use your old X99 board for any of the Core-X CPUs. 

Like the i7-7700K, it’s a quad-core CPU with Hyper-Threading. Unlike the higher-end Core-X CPUs, there’s no support for the new Turbo Boost Max 3.0, instead relying on the standard boost to hit 4.5GHz. The number of PCIe lanes has been slashed compared to upper-end Core-X CPUs, with just sixteen to play with. Unlike the i9-7900X, this CPU only supports dual channel memory as opposed to the quad-channel memory of the other CPU. So, that X299 motherboard you’ll need to buy, which comes with eight memory slots, will see four of them go to waste. Also, the integrated graphics of the i7-7700K have been disabled, which doesn’t make a great deal of sense to us. Of the 2066 pins on the chip, about 1000 of them aren’t even used. 

Another CPU, another chipset

Unlike AMD, who generally like to keep their new CPUs compatible with existing motherboard chipsets for as long as possible, Intel loves to release a new chipset with each new CPU release. In the case of the Core-X it’s the X299 chipset, which features the new LGA 2066 socket. It also supports quad-channel memory, with an official frequency of DDR4-2666MHz, and a maximum amount of 128GB. However, some Core-X CPUs only officially support DDR4-2400MHz, such as the It’s worth pointing out that Ryzen’s new chipset is the X399, so try not to buy the wrong chipset when you’re buying a board for your Core-X. We think this is a bit cheeky of AMD, as it simply confuses customers. 

One of the main differences with the new X299 over the previous X99 chipset is the use of a High Speed IO design, which it used to only offer on its Z series of motherboards. This makes the chipset act like one large switch; the DMI 3.0 link from the CPU is basically a PCIe 3.0 x 4 link, and the chipset itself could support up to 24 lanes of PCIe 3.0. Motherboard makers would then use the PCIe lanes from the chipset for the likes of M.2 slots, USB, and Ethernet. 

X299 now uses the same design, and increases the DMI 2.0 of the X99 to the speed of the DMI 3.0 of the Z-series. This is a large increase in bandwidth, which is why the top-end Core-X CPUs now offer up to 44 lanes of PCIe 3.0 to play with. This will allow motherboard manufacturers much more flexibility in terms of the number of M.2, USB, SATA and other features. 

X299 also supports Intel’s new Optane hard drive caching technology; though that’s not really a huge benefit given our issues testing Optane in the past. Hopefully the technology will mature to the point where it’s simple plug and play, without the need for special disk formatting or only supporting the main OS drive. 

In terms of connectivity, X299 natively supports ten USB 3.0 and eight SATA 3 ports. We’ll obviously see vendors increasing this though, given how many PCIe lanes they have to work with now. The X299 also includes Intel’s new Virtual Raid on CPU (VROC), but there’s a catch. You’ll have to pay extra for a tiny key that inserts into the motherboard to enable it. Given that it appears VROC support is already built into the CPU and X299, this seems rather stingy. It is rather cool tech though, allowing up to twenty drives to be synched into one bootable RAID array. 

Overclocking for all

Every Core-X CPU will ship factory unlocked, while the X299 chipset supports full multiplier and base clock frequency adjustments. This means overclockers should have a field day with this chip, although it does seem that Intel has once again used paste between the heat spreader and the silicon, so delidding will likely become popular amongst extreme overclockers. Currently the world record for Core-X overclock is 5.7GHz, using LN2 cooling and an Asus Rampage motherboard. We noticed on all of our boards that there’s an extra 4-pin power input on the board; we’re not sure if this is for overclockers, or for the upcoming 18-core behemoth. 

To Core-X or not to Core-X?

As our benchmarks show, in many instances, the i9-7900X had a sizeable lead in performance over the Ryzen 7 1800X. Yet there were also a handful where AMD’s chip wasn’t too far behind, which is very impressive considering it’s half the price. There’s also the issue of the cost of motherboards; it’s possible to buy a Ryzen 7 compatible board for around $250, while X299 boards start around the $450 point. Therefore the total cost of ownership for a Ryzen 7 1800X system is less than half that of the Intel i9-7900X system. 

If you’re looking for the ultimate in performance, there’s no denying that the i9-7900X is currently the fastest consumer CPU on the desktop. However, if you’re looking for a decent balance between price and performance, the Ryzen 7 1800X puts up a decent fight for half the cost, so your decision is going to be based entirely on budget. 

Whichever one you go for, it’s a blessing that we finally have competition once again in the CPU market. Intel’s monopoly has been shaken, and that can only mean good things for consumers. With even bigger, faster chips on the way, both companies now have more motivation than ever to deliver the best possible product, at the best possible price. 


How we tested 

We recently did in-depth testing of AMD’s Ryzen 5 and 7 chips, so mimicked our tests for these CPUs as closely as possible, right down to the driver version. The meant we used the same SSDs, Ballistix memory, though we did have to change the cooler to fit the larger socket. Our test GPU was the Aorus GeForce GTX 1080 OC, and we set all game tests to the lowest resolutions to ensure the GPU wasn’t the bottleneck. 

Looking at the results, it’s obvious that the i9-7900X is a monster, taking out the top spot in nearly every test. We were especially surprised at its gaming results, where the slower frequency should have seen it perform slower than the i7-7700K. It’s obvious the architectural improvements have made a difference to performance. 

As for the i7-7740X, this was less than impressive, basically equalling the i7-7700K in most tests. There’s not much point in upgrading to the i7-7740X right now, unless you plan to climb the Core-X ladder further down the road. 

When testing the motherboards, we installed the overclocking software that came with each board, but as you’ll see the vast majority of these did not work, likely due to the issues with Turbo Boost Max 3.0. We’re sure speeds of 4.8GHz and above should be possible with manual overclocks. 



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