The Intel Kaby Lake-X i7-7740X Review

Author: SKYMTL
Date: June 18, 2017
Product Name: i7-7740X
Part Number: i7-7740X
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Intelís Skylake-X Under The Microscope

A few days ago I mentioned on Twitter this is likely one of the most confusing launches in recent history. I wasnít kidding. Not only is Intel launching a brand new lineup of high end desktop (HEDT) processors in Skylake-X but they are also rolling the mid-level Kaby Lake architecture into the mix in the form of Kaby Lake-X. This is the first time their HEDT platform will feature two different processor architectures and that causes some issues due to wildly differing capabilities offered by each.

To give you a quick idea of this situation before I go into a few more of its nuances, everything from the PCI-E lane allotments to the PCHís I/O layouts to the platformís feature set will change depending on which processor you have installed. You will also need to be careful about memory installation since the underlying architecture of each processor handles DIMM assignments differently. Iím going to do my best to go through this one blow at a time but keep in mind there are still a lot of parallels you can draw between these new processors and their Broadwell-E predecessors.

One of the hallmarks of Skylake-X series processors is a carry-over from the aforementioned Broadwell-E generation: Intel Turbo Boost Max 3.0. Basically ITBM 3.0 determines which specific cores on your particular CPU are capable of running at higher speeds during lightly threaded workloads and accelerates their frequency level. It does so by actively monitoring temperatures and how many cores are being engaged in order to estimate input current and power consumption. If there is available headroom, the active core(s) will have more leeway to operate faster.

In essence this grants a third gear above and beyond the typical Base and Turbo rates we are all used to seeing but where Skylake-X processors differ is how many cores will boost to the stated ITBM 3.0 frequency. Whereas Broadwell-E featured a single ďbestĒ core, thereís now the possibility that up to two cores will reach significantly higher speeds. That in itself could prove to be a key differentiating factor in gaming where many of todayís most-popular titles tend to benefit from higher speed, lower core count designs. It also happens to highlight why CPUs in the Skylake-X family may prove to be poor value companions for gamers.

Skylake-X actually has several core architecture updates including a new Xeon-derived ďMeshĒ topology which seems to be very much like AMDís Infinity Fabric. This so-called mesh effectively replaces the less scalable ring bus architecture with a highly adaptable interconnect backbone that uses a series of more direct paths between the I/O controllers, memory, cache and cores. This is supposed to not only reduce on-chip latency but it will also help Intel expand and contract Skylake-Xís core layout as needed with a minimum of intervention.

The move to this layout also improves accessibility to the chipís on-die last level cache (LLC). Efficiently communicating with this large block of cache is a key aspect for application developers and in this case all o the cache banks can be accessed with a bare minimum of latency fluctuation. As a result, Intel has also been able to revise their caching hierarchy in a pretty meaningful way.

Previous generations of HEDT processors featured a shared last level cache size of up to 2.5MB per core and 256KB per core of integrated mid level cache. That structure is now changing with an LLC layout of up to 1.375 MB/core which may cause some issues for highly threaded workstation applications that tend to mercilessly pound away at that shared LLC block. However, the new low latency mesh interconnect could theoretically offset some of that bottleneck through more efficient communication.

In order to combat any perceived caching discrepancy, Intel has quadrupled the MLC within each core to a whopping 1MB. That means a 10 core processor will have a full 10MB of MLC to draw upon in demanding situations.

Letís start things off with the thousand pound gorilla in the room: the four processors which sit atop the chart above but donít have any real specifications other than core counts and stratospheric prices. In many ways these were announced as a hedge against AMDís impending Threadripper and nothing more. At this point it looks like the i9-7920X, i9-7940X, i9-7960X and i9-7980XE will have their launches split between the second half of 2017 and Q1 2018. In the meantime, their true performance is anyoneís guess since final frequencies are still being determined by Intelís labs. I wonít spend any more time on those until weíre closer to launch.

Moving towards the processors that will actually be available come launch and we have the i9-7900X which is meant to take over from the i7-6900K while offering more cores, additional threads, 4 more PCI-E lanes and higher clock speeds. As a matter of fact, above all else this processor highlights the downwards pressure a resurgent AMD is having upon Intelís pricing structure. A cool thousand bucks is a lot to ask for any piece of computer hardware these days but the 10 core, 20 thread i9-7900X does seem to have a lot more performance on tap than its predecessor while costing about $100 less. With that being said I think this looks like a ďfairĒ price simply because the 6900K was so over priced.

The i9-7900Xís feeds, speeds and power consumption point towards a broad refinement in Intelís 14nm manufacturing process. Base, Turbo and Turbo 3.0 frequencies are respectively 300MHz, 800MHz and 500MHz faster than the similarly laid out i7-6950X. Meanwhile, supported memory speeds have increased to 2666MHz and TDP remains at 140W which is quite impressive for such a capable CPU.

Whereas Intelís goal with the i9-7900X seems to be pretty clear cut, venture into the i9-78xx series lineup and things get muddy very, very fast. As a matter of fact, the first time I saw the specifications for the i7-7820X and i7-7800X, I thought there was a misprint but my fears were quickly confirmed after a quick email to Intel.

Letís start with the i7-7820X, a processor that at first seems to follow directly in the footsteps of the i7-6850K. As is the trend for Skylake-X parts, the $600 7820X gets an upgrade to 8 cores and 16 threads but and operates at much higher Turbo and Turbo 3.0 frequencies. It also gets the benefit of that double-fisted best core ITBM 3.0 technology. Unfortunately, while the i7-6850K had access to 40 PCIe lanes, this new CPU gets castrated down to a mere 28 lanes which makes dual x16 graphics operation impossible without an expensive lane multiplier on the motherboard. Its officially supported memory speed gets cut to 2400MHz as well. So the question is simple: are you willing to sacrifice potential dual GPU throughput for a higher core count? If only Intel didnít ask you to make that decision.

The i7-7800X had some massive shoes to fill since the i7-6800K was arguably one of the most popular SKUís in the Broadwell-E lineup. Well it looks like when creating the replacement i7-7800X, Intel chould have trimmed a bit off of the i7-7820X but instead used a gas powered weed whacker. This CPU is cut down to the same 6 cores and 12 threads as its forefather, has 28 PCIe lanes and Ėno, that isnít an error in the charts- even gets Turbo Boost Max 3.0 cut out of its equation. Luckily it does operate at up to 4.0GHz but if you are currently rocking an i7-6800K it looks like youíll be safe from the upgrade bug for now.

The 7800-series are extremely important to the success of this platform for Intel since their specifications lead to direct competition against AMDís higher-end Ryzen processors. The $599 i7-7820X will find itself going head to head against the less expensive yet frequency deficient 1800X and 1700X. Meanwhile the $389 6 core, 12 thread i7-7800X could find itself in tough company against the 16 thread 1700X and 1700.

While it does look like Intel is opening the door to a few more SKUs (looks like there will be an i5 lineup as well) by taking a hacksaw to their once-sensible HEDT lineup, the reason behind this seemingly nonsensical move may be straightforward. It can be summed up in two and a half words: Kaby Lake-X. Letís jump ahead and see why that is.

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