Building a PC is an experience worth having. Finding out what works with what and putting it all together is an experience, and the first time always gives a sense of achievement and accomplishment. In the high-end desktop space, even more so: trying not to break your first $500+ CPU can be akin to feeling like a surgeon. Following the HEDT space can be a journey, especially after five years of iterative updates we are seeing something special happening in 2017. Intel, the incumbent, is changing its 2017 strategy in a few ways which means there is more to understand, and in the future, and also means it is set to release 18-core consumer processors. Today is the first part of that release, with the new Skylake-X processors: the Core i9-7900X, the Core i7-7820X and the Core i7-7800X. These throw a few curveballs into the mix which are worth walking into.

Back at Computex, Intel announced its new high-end desktop (HEDT) platform code named Basin Falls. There are three elements to Basin Falls: the new X299, chipset which brings a number of enhancements from the more mainstream consumer line, a set of Skylake-X processors based on the Skylake-SP microarchitecture (and slightly different from the mainstream Skylake-S processors launched in 2015) from 6 cores to 18 cores, and a pair of Kaby Lake-X processors, reusing the Kaby Lake-S silicon launched earlier this year but with a bit more frequency and power consumption.

We covered all three parts in our launch pieces (linked below), but here is a quick recap.

Intel Announces Basin Falls: The New High-End Desktop Platform and X299 Chipset
Intel Announces Skylake-X: Bringing 18-Core HCC Silicon to Consumers for $1999
Intel Announces
Kaby Lake-X Processors: High-End Desktop Getting the Latest Microarchitecture

Skylake-X Today: Three CPUs, Up to 10 Cores, Lower Pricing than Broadwell-E

One of the big criticisms from the launch of Broadwell-E, the platform before Skylake-X, was that Intel significantly increased prices over the preceding generation. Nominally consumers were used to the fact that the top chip in the stack was $999 to $1099, and rather than readjust the 6, 8 and 10 core parts to do so, Broadwell-E pushed the 10-core Core i7-6950X to ~$1721, in order to claim parity with the enterprise processors. Users who scoffed at that price will be pleased to hear that the Skylake-X processors launching today are priced more in line with Intel's traditional HEDT chips.

Skylake-X Processors (Low Core Count Chips)
  Core i7-7800X Core i7-7820X Core i9-7900X
Cores / Threads 6/12 8/16 10/20
Base Clock 3.5 GHz 3.6 GHz 3.3 GHz
Turbo Clock 4.0 GHz 4.3 GHz 4.3 GHz
TurboMax Clock N/A 4.5 GHz 4.5 GHz
L3 8.25 MB 11 MB 13.75 MB
PCIe Lanes 28 44
Memory Channels 4
Memory Freq DDR4-2400 DDR4-2666
TDP 140W
Price $389 $599 $999

The Core i9-7900X is the 10-core processor and set to have a tray price of $999, which means the shelf price will be around $1049-$1099. The Core i9-7900X is also the only one with a full complement of 44 PCIe lanes from the processor, as Intel is restricting this feature to the higher cost parts of the stack in order to further differentiate it from the cheaper i7-7800 series. This processor is quite aggressive in its specifications – normally the top LCC processor is clocked down, using the extra cores as the main reason for purchase, but here Intel is supporting a maximum turbo frequency of 4.3 GHz, or up to 4.5 GHz with the new-ish favored core mode. The base frequency is lower than the other CPUs to compensate, at 3.3 GHz, but we saw an all-core frequency at 4.0 GHz in our testing. This all comes in a 140W TDP, with support up to DDR4-2666 in quad channel mode at 1 DIMM per channel (DDR4-2400 at 2DPC).

The Core i7-7820X sits below, exchanging two of the CPU cores and some PCIe lanes for a higher base frequency. This is an eight-core part, which reduces the total cache as well, but has a base frequency of 3.6 GHz to compensate. The PCIe lanes are reduced from 44 to 28 as part of Intel’s product segmentation strategy, although Intel notes this is still enough for a single GPU and three PCIe 3.0 x4 devices (such as storage) directly attached to the processor. DRAM support is the same as the Core i9 at DDR4-2666, as is also the TDP at 140W. Coming in at $599 represents a bit of a step from the 10-core down to the 8-core. This price will arguably draw a good number of users who would rather direct that $400 to something else in their system with the only deficit being two cores and a proper x16/x16 layout for dual video cards.

The bottom processor is the Core i7-7800X, with six cores, a lower frequency (3.5 GHz base, 4.0 GHz turbo, no favored core support), 28 PCIe lanes, and support only up to DDR4-2400. While categorically ‘the runt’ of the litter, Intel has priced this part at $389, only $50 more than the mainstream consumer quad-core overclocking processors. Along with a slight cost increase for the new X299 motherboards, users looking to move from the mainstream to the bottom rung of the high-end desktop can do so with around $120-$150 extra for CPU+motherboard, and then a bit more if the users wants to use quad channel memory (these processors work in dual channel as well). As the low-end part, traditionally users may point to it as a potential overclocking processor – we unfortunately did not have time to test our sample for overclocking, but I wouldn’t be surprised to see it hit the same frequencies as the other two processors fairly easily.

Competition and Market

In previous years, Intel only had one serious angle of competition for the HEDT platform: itself. As it introduced new generation parts, the older generation could (sometimes) be picked up cheaper, making the older generation more enticing. But as it stands, for the first time in a long time, Intel has three main sources of competition for the X299 platform.

First is as mentioned, Intel’s older platform in Broadwell-E (or even Haswell-E). Broadwell-E, aside from the steep pricing, is now a solid platform, with extensive motherboard support and well-known functionality. Intel has not officially dropped the prices of the older processors, which unless the retailers decide to shift stock wholesale might discourage users going for brand new CPUs, but the ecosystem for BDW-E is mature.

Comparison: Core i9-7900X vs.
i7-6950X vs i7-5960X
Features Intel Core i9-7900X Intel Core i7-6950X Intel Core i7-5960X
Core Skylake-SP Broadwell Haswell
Cores/Threads 10 / 20 10 / 20 8 / 16
Base/Turbo 3.3 / 4.3 GHz 3.0 / 3.5 GHz 3.0 / 3.6 GHz
PCIe 3.0 Lanes 44 40 40
L2 Cache/core 1 MB 256 KB 256 KB
L3 Cache 13.75 MB 25 MB 20 MB
TDP 140 W 140 W 140 W
Price (MSRP) $999 $1723 $999

Second is AMD’s recently released Ryzen set of CPUs. As the first new serious entry into the HEDT space for AMD in almost five years, along with a new x86 core, AMD offered similar-ish performance to Broadwell-E in many aspects (within a few percent), but at half the price or better. The Ryzen CPUs still had other limits – dual channel memory, only sixteen PCIe lanes, limited IO from the chipset, and a miasma surrounding the launch with motherboards and memory support; but several months on the ecosystem for Ryzen is fairly solid and still a new and exciting prospect for the HEDT crowd. For $60 less than the price of the Core i7-7800X, a six-core Intel processor, AMD offers the Ryzen 7 1700, which runs in at 8 cores at slightly lower frequency, with cheaper motherboards as well.

Comparison: Core i7-7800X vs. Ryzen 7 1700
Intel
Core i7-7800X
Features AMD
Ryzen 7 1700
6 / 12 Cores/Threads 8 / 16
3.5 / 4.0 GHz Base/Turbo 3.0 / 3.7 GHz
28 PCIe 3.0 Lanes 16
8.25 MB L3 Cache 16 MB
140 W TDP 65 W
$389 Price (MSRP) $299

Both Intel and AMD would argue the merits of the platforms vs. cost, but Intel still this as an angle for competition. Similarly, the 6-core Core i7-7820X at $599 goes up against the 8-core $499 Ryzen 7 1800X.

Comparison: Core i7-7820X vs. Ryzen 7 1800X
Intel
Core i7-7820X
Features AMD
Ryzen 7 1800X
8 / 16 Cores/Threads 8 / 16
3.6 / 4.3GHz
(4.5 GHz TMax)
Base/Turbo 3.6 / 4.0 GHz
28 PCIe 3.0 Lanes 16
11 MB L3 Cache 16 MB
140 W TDP 95 W
$599 Price (MSRP) $439

Third is AMD’s future HEDT (or Super High-End Desktop, SHED) platform. Announced in the run up to Computex, AMD is set to offer a new X399 chipset with ThreadRipper processors up to 16-core and with 60 PCIe lanes for graphics (plus four for the chipset, which is why AMD keeps saying 64). AMD is using two of its consumer Zeppelin silicon dies on the same package to get up to 16-cores, and has a new socket planned due to the increase in PCIe support. Having had Intel moving from 6 to 8 to 10 cores on the HEDT space over the last 5-6 years meant that AMD announcing a 16-core part was a big enough jolt to this market such that Intel has to provide a response. Pitting a 10-core CPU such as the Core i9-7900X against a 16-core AMD CPU means that AMD would win most the high-throughput heavily-threaded benchmarks, despite perhaps being lower frequency and higher power. For the HEDT/SHED crowd, sometimes it’s all about how quick you can compute. AMD is set to launch the X399 platform and ThreadRipper CPUs in the summer, so we’re still light on details until then, but given AMD's disruptive nature, there's a real risk to Intel that AMD will once again undercut Intel’s equivalent 16-core pricing by a large amount.

Comparison: Core i9-7900X vs. 
i7-6950X vs i7-5960X
Features AMD Ryzen 7 1800X Intel Core i9-7900X AMD ThreadRipper
Core Zen Skylake-SP Zen
Cores/Threads 8 / 16 10 / 20 16 / 32
Base/Turbo 3.6 / 4.0 GHz 3.3 / 4.3 GHz ?
PCIe 3.0 Lanes 16 44 60
L2 Cache/core 512 KB 1 MB 512 KB
L3 Cache 16 MB 13.75 MB 32 MB
TDP 95W 140 W >140W ?
Price (MSRP) $439 $999 ?!?

What Is This Review

This review comes in two big meaty chunks to sink your teeth into. The first part is discussing the new Skylake-X processors, from silicon to design and covering some of the microarchitecture features, such as AVX-512-F support and cache structure. As mentioned, Skylake-X has some significantly different functionality to the Skylake-S core, which has an impact on how software should be written to take advantage of the new features.

The second part is our testing and results. We were lucky enough to source all three Skylake-X processors for this review, and have been running some regression testing of the older processors on our new 2017 testing suite. There have been some hiccups along the way though, and we’ll point them out as we go.

An extra morsel to run after is our IPC testing. We spend some time to run tests on Skylake-S and Skylake-X to see which benchmarks benefit from the new microarchitecture design, and if it really does mean anything to consumers at this stage.

It should be noted that Intel did not provide all the CPUs for this review. As with standard Intel policy, only the top CPU came direct from Intel. All CPUs in this review are classified as engineering samples for partner testing and not for resale, although they are identical to retail CPUs in performance.

The Basin Falls Platform: X299, SKL-X, & KBL-X
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  • Tephereth - Tuesday, June 20, 2017 - link

    "For each of the GPUs in our testing, these games (at each resolution/setting combination) are run four times each, with outliers discarded. Average frame rates, 99th percentiles and 'Time Under x FPS' data is sorted, and the raw data is archived."

    So... where the hell are the games benchmarks in this review?
  • beck2050 - Tuesday, June 20, 2017 - link

    The possibility of the 18 core beast in the upcoming Mac Pro is really exciting for music pros.
    That is a tremendous and long overdue leap for power users.
  • drajitshnew - Tuesday, June 20, 2017 - link

    "... and only three PCIe 3.0 x4 drives can use the in-built PCIe RAID"
    I would like to know which raid level you would use. I can't see 3 m2 drives in raid 1, and raid 5 would require access to the cpu for parity calculations. Then raid 0 it is. Now, which drives will you use for raid 0, which do not saturate the DMI link for sequential reads? And if your workload does not have predominantly sequential reads, then why are you putting the drives in raid.
  • PeterCordes - Tuesday, June 20, 2017 - link

    Standard motherboard RAID controllers are software raid anyway, where the OS drivers queue up writes to each drive separately, instead of sending the data once over the PCIe bus to a hardware RAID controller which queues writes to two drives.

    What makes it a "raid controller" is that you can boot from it, thanks to BIOS support. Otherwise it's not much different from Linux or Windows pure-software RAID.

    If the drivers choose to implement RAID5, that can give you redundancy on 3 drives with the capacity of 2.

    However, RAID5 on 3 disks is not the most efficient way. A RAID implementation can get the same redundancy by just storing two copies of every block, instead of generating parity. That avoids a ton of RAID5 performance problems, and saves CPU time. Linux md software RAID implements this as RAID10. e.g. RAID10f2 stores 2 copies of every block, striped across as many disks as you have. It works very well with 3 disks. See for example https://serverfault.com/questions/139022/explain-m...

    IDK if Intel's mobo RAID controllers support anything like that or not. I don't use the BIOS to configure my RAID; I just put a boot partition on each disk separately and manage everything from within Linux. IDK if other OSes have soft-raid that supports anything similar either.

    > And if your workload does not have predominantly sequential reads, then why are you putting the drives in raid.

    That's a silly question. RAID0, RAID1, and RAID5 over 3 disks should all have 3x the random read throughput of a single disk, at least for high queue depths, since each disk will only see about 1/3rd of the reads. RAID0 similarly has 3x random write throughput.

    RAID10n2 of 3 disks can have better random write throughput than a single disk, but RAID5 is much worse. RAID1 of course mirrors all the writes to all the disks, so it's a wash for writes. (But can still gain for mixed read and write workloads, since the reads can be distributed among the disks).
  • Lieutenant Tofu - Tuesday, June 20, 2017 - link

    I wonder why 1600X outperforms 1800X here on WebXPRT. It's not a huge difference, but I don't see why it's happening. 6-core vs. 8-core, 3.6 GHz base, 4.0 GHz turbo. This presumably runs in just one thread, so performance should be nearly identical. The only reason I can think of is less contention across the IF on the 1600X due to less enabled cores, but don't see that having a major effect on a single-threaded test like this one.

    Maybe 1600X can XFR to a little higher than the 1800X.
  • Eyered - Tuesday, June 20, 2017 - link

    Did they have any issues with heat at all?
  • mat9v - Tuesday, June 20, 2017 - link

    If that were so everyone would be using HEDT instead of 4c/8t CPUs
  • mat9v - Tuesday, June 20, 2017 - link

    Then why again why aren't every workstation consist of dual cpu xeons? If the expense is so insignificant compared to how much faster machine will earn...
  • mat9v - Tuesday, June 20, 2017 - link

    I'm just wondering how did 7900X menage to stay within 140W bracket during Prome95 tests when in other reviews it easily reached 250W or more. Is it some internal throttling mechanism that keeps CPU constantly dynamically underclocked to stay within power envelope? How does such compare to forced 4Ghz CPU clock?
  • mat9v - Tuesday, June 20, 2017 - link

    And yet in conclusion you say to play it safe and get 7900X ?
    How does that work together?

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