Introduction

Intel gave its high-end desktop (HEDT) platform a much needed update this year with the Core X series consisting of 6-core, 8-core, 10-core, 12-core, and future 16-core and 18-core processors to cater to the pro-sumer crowd that just wants raw CPU power and platform connectivity without having to pay the Xeon tax (in exchange for reliability and ECC memory support). They've also brought PC enthusiasts the option of building future-proof rigs they don't have to upgrade for over half a decade.

Unlike previous generations of HEDT chips which were all positioned under a single Core i7 brand, Intel significantly changed its nomenclature. The "X" in the model number now denotes an HEDT model, one which features an unlocked base-clock multiplier, and the sub-brand itself has been expanded to include Core i7, the new Core i9, and even Core i5. As a general rule of thumb, SKUs with wide 44-lane PCI-Express interfaces are pushed up to the Core i9-79##X brand, while Core i7-78##X chips give you core-counts between 6 and 8 with 28-lane PCI-Express. These chips are built on the large "Skylake-X" silicon, which is a derivative of the "Skylake" micro-architecture, and feature significant architectural changes and not just linear increases in core counts over the mainstream desktop "Skylake-S" silicon.

In the wake of the AMD Ryzen 7 series bringing HEDT-like multi-threaded performance to the mainstream-desktop AM4 platform, Intel appears to have clearly panicked, rolling out the Core i5-7640X (which we are reviewing today) and the Core i7-7740X processors based on the "Kaby Lake-X" silicon. These chips are priced almost on-par with the LGA1151 Core i5-7600K and i7-7700K, and de-lidding by the community has shown that Intel basically placed the quad-core "Kaby Lake-S" die on the LGA2066 package to make these chips - but their only selling-point is their vertical upgrade path to larger multi-core processors.



The Core i5-7640X and i7-7740X have nearly the same stock clock speeds as their LGA1151 siblings, but their TDP has been bumped up to 112W from 91W, which many took as an indicator towards improved overclocking potential. Since the LGA2066 platform lacks onboard graphics, you lose out on the integrated graphics present on the "Kaby Lake" die, which could otherwise prove useful for troubleshooting. At the same time, you get the same dual-channel memory interface, meaning that half the memory slots on your socket LGA2066 motherboard won't function unless it happens to be one of the few boards designed only for Kaby Lake-X, which would have it support a dual-channel interface while having four slots in total; and you get all of 16 PCI-Express gen 3.0 lanes, which is only good for the amount of connectivity that would have you opt for the LGA1151 platform in the first place. As such, some expansion slots on your motherboard will either be disabled or run at much lower bandwidth with these chips.

In addition, the specs table below helps reveal more information. You lose out also on the silicon-level goodies Intel introduced with "Skylake-X", such as 1 MB of L2 cache per core, and the mesh-topology, which vastly improves inter-core communication while also reducing core-uncore latencies. As with the LGA1151 "Kaby Lake" chips, you only get 256 KB of L2 cache per core, the classic ring-bus topology, and even lose out on integrated graphics. As if that isn't worse, the Core i5-7640X even features a relatively small 6 MB of L3 cache and lacks HyperThreading. These are items that go beyond subjective reasoning; however, let us refrain on making a conclusion until all the tests are concluded and the results summarized.

To sum up, in this review, we put the Core i5-7640X, the $240 price of entry to the HEDT platform, to the test. We paired it with 16 GB of dual-channel memory and a GeForce GTX 1080 graphics card to see where Intel's Core i5-7640X stands in comparison to Ryzen and the LGA1551 Kaby Lake processors.

A Closer Look

The Core i5-7640X comes in the premium-looking Core X family retail packaging, which means you get a case badge that's visibly different and more premium-looking than the Core i5 LGA1151 series. Sadly, the case badge and some documentation are the only other things you get inside the box, apart from the processor. You will have to install your own socket LGA2066-compatible cooling solution (which isn't included in the processor's price).


The LGA2066 package is the same size as previous-generation LGA2011(v3) packages, with different key notches. This also means that the LGA2066 socket itself has the same cooler mount-hole spacing as the older socket, and you have plenty of aftermarket coolers to choose from. As its name suggests, this package has a land-grid array (LGA) with a pin-count of 2,066 pins. The 126 mm² "Kaby Lake" die is located dead-center and is much smaller than the "Skylake-X" die found on other Core X family processors, so focusing your cooling on the center with a tiny amount of TIM should do the trick.


As we mentioned earlier, the LGA2066 socket has the same mount-hole spacing as previous-generation LGA2011(v3), and you should, as such, be able to use any compatible cooler.

The "Kaby Lake-X" Silicon

As we mentioned in the introduction, the Core i5-7640X and its sibling, the i7-7740X, are essentially quad-core "Kaby Lake" dies placed on LGA2066 packages, which means that apart from being for a different socket and losing out on integrated graphics, they are practically identical to 7th generation Core "Kaby Lake" processors. The "Kaby Lake-X" die in itself is optically identical to the "Skylake-S" quad-core die, except that is built on the newer 14 nm+ process, which allows higher transistor drive current, letting Intel increase clock speeds by up to 15 percent at minimal power/thermal cost.

The "Kaby Lake-X" die physically features just four CPU cores, with the same essential cache hierarchy as older generations of Core processors, where the core has an arbitrary 256 KB of faster dedicated L2 cache, while the die itself either has 1.5 MB/core or 2 MB/core of shared L3 cache. This is in contrast to the other LGA2066 "Skylake-X" processors, which implement Intel's biggest change in cache-organization in close to a decade, featuring 1 MB of faster dedicated L2 cache per core, and 1.375 MB/core of shared L3 cache.



Another major "Skylake-X" feature not found on the "Kaby Lake-X" die is the new mesh-topology, where the various components of the processor are interconnected at multiple points that make up a "mesh" as opposed to the "ring-bus" topology Intel has been using since "Nehalem" (circa 2008). The mesh topology is designed to improve inter-core communication as the ring-bus approach can't keep up with increasing core counts (ring stops) without adding an intolerable amount of latency. Since "Kaby Lake-X" only features four physical cores, this won't be much of a deal. Since the LGA2066 platform lacks onboard graphics as a feature, the integrated Gen 9.5 graphics core of the "Kaby Lake-X" silicon is dead weight.



Intel's "Kaby Lake" die only features a dual-channel DDR4-integrated memory controller, and the Core i5-7640X will only support up to 64 GB of dual-channel memory; only half the memory slots on your motherboard will work (the manual will tell you which ones). What's more, the "Kaby Lake" die has a narrower PCI-Express gen 3.0 root complex with only 16 lanes allocated to PEG (PCI-Express Graphics) and four to the DMI 3.0 chipset bus. Certain PCIe and M.2 slots on your motherboard will outright not work. Those that do might do so at a lower-than-expected bandwidth. If you only have one graphics card, install it in the topmost slot, as that one tends to have the full x16 wiring to the CPU. When in doubt, consult your motherboard manual.

For the Core i5-7640X, Intel continues to keep HyperThreading disabled, making it the first Intel HEDT chip since 2008 to lack it. The L3 cache amount is 6 MB, which is on par with its LGA1151 siblings. The only on-paper difference between this chip and the i5-7600K is its slightly higher clock speed, which is 4.00 GHz instead of the 3.80 GHz clock of the i5-7600K. The Turbo Boost clock remains unchanged at 4.20 GHz, and the unlocked base-clock multiplier lets you overclock the chip. The "Kaby Lake-X" quad-core chips also lose out on the Turbo Boost Max 3.0 feature of the "Skylake-X" chips, which enables automatic overclocking beyond the max Turbo Boost frequency and depends on your cooling setup's effectiveness. And yet, the TDP of these chips has been bumped up to 112W for some reason. It had better indicate higher overclocking headroom.

The LGA2066 Platform

People pick HEDT platforms not only for higher core-counts, but increased platform connectivity, in the form of more PCI-Express lanes, support for more memory, more storage options, etc. The LGA2066 platform in itself covers all the bases with connectivity. You can run up to four graphics cards for multi-GPU greatness, up to eight DDR4 memory modules for a total of 128 GB of quad-channel memory, and a plethora of other onboard devices, thanks to the higher PCI-Express budget. Unfortunately, the Core i5-7640X and Core i7-7740X neither deliver on the promise of more cores or connectivity than a mainstream desktop. When it comes to platform connectivity, they bring nothing new to the table since their PCI-Express lane budget is the same as the LGA1151 platform.

The Intel HEDT platform originally gave you a high PCI-Express lane budget across the lineup. The company then began segmenting its processors by giving the cheaper processors fewer PCI-Express lanes (28 vs. 44), which still ended up being higher than the 16 lanes put out by mainstream-desktop Core processors. The Core i5-7640X is essentially a mainstream-desktop processor in high-end desktop clothing, and hence gives you that very limited lane budget. LGA2066 motherboards come with PCI-Express auto-switching to either cope with 28-lane or 44-lane root complexes, but when a 16-lane processor such as the i5-7640X is installed, certain slots, onboard devices, and M.2 slots will be disabled because those 16 lanes are wired to the PCI-Express x16 slots.