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Skylake: Intel Core i7-6700K

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Intel’s latest desktop CPU generation boasts improved CPU/iGPU performance, superior energy efficiency. Combined with a new chipset architecture that supports DDR4 and allows for more features, Skylake represents the strongest “tock” from Intel’s processor upgrade cycle since Sandy Bridge.

September 14, 2015 by Lawrence Lee

Product
Intel Core i7-6700K
LGA1151 Processor
Manufacturer
Street Price
US$350

Since the launch of Sandy Bridge in 2011, Intel’s tick-tock microprocessor architecture upgrade cycle has been decidedly light on the tock, the distinctive thump corresponding to a more substantial update than the quieter tick preceding it. Despite the die shrink from 32nm to 22nm, Ivy Bridge represented a fairly minor upgrade in performance and efficiency. Its successor, Haswell necessitated a socket change but the level of improvement was more or less the same. The subsequent tick, Broadwell, was even more disappointing as it focused on the low-end embedded/mobile market.

“K” Chips Comparison (Haswell vs. Skylake)
Model
i5-4670K
i5-4690K
i5-6600K
i7-4770K
i7-4790K
i7-6700K
Socket
LGA1150
LGA1150
LGA1151
LGA1150
LGA1150
LGA1151
Memory Support
DDR3
DDR3
DDR3L
DDR4
DDR3
DDR3
DDR3L
DDR4
Cores / Threads
4 / 4
4 / 4
4 / 4
4 / 8
4 / 8
4 / 8
CPU Clock (Base/Turbo)
3.4 / 3.8 GHz
3.5 / 3.9 GHz
3.5 / 3.9 GHz
3.5 / 3.9 GHz
4.0 / 4.4 GHz
4.0 / 4.2 GHz
L3 Cache
6MB
6MB
6MB
8MB
8MB
8MB
Graphics
HD 4600
HD 4600
HD 530
HD 4600
HD 4600
HD 530
Execution Units
20
20
24
20
20
24
Max GPU Clock
1200 MHz
1200 MHz
1150 MHz
1250 MHz
1250 MHz
1150 MHz
TDP
84W
88W
91W
84W
88W
91W
Price (USD)
$230
$230
$240
$330
$300
$350

Skylake is the codename for this year’s tock, built on the same 14 nm process as Broadwell, but offered to mainstream desktop users in a new socket with an extra pin, LGA1151. For the initial launch, Intel has chosen to put its best foot forward, presenting a pair of “K” series chips with unlocked multipliers aimed at enthusiasts first and foremost. As usual, the differentiation between Core i7’s and i5’s is the presence of Hyper-threading and the amount of L3 cache. The i5-6600K appears to be the direct analog of the popular i5-4690K while the i7-6700K is similar to the i7-4790K, except for an unusually low Turbo Boost of just 200 MHz.

The new processors are 91W parts, slightly higher than the last generation, possibly due to the upgraded integrated graphics. Intel Graphics HD 530, the successor to HD 4600, should deliver a noticeable performance increase despite having a slightly lower maximum clock speed. It’s equipped with an additional four execution units, and in all likelihood, will be paired with faster DDR4 memory. For Skylake motherboard makers have the choice between dual channel DDR4 and DDR3L memory. Standard DDR3 is not officially supported as its voltage range is higher but there are a handful of models offering the regular standard.

Under the hood, the biggest change is the removal of the integrated voltage regulator, which improved efficiency and lowered costs but ultimately generated too much heat at high clock speeds, limiting the overclockability of Haswell/Broadwell chips. For Skylake, the responsibility of voltage regulation is returned to the motherboard, reducing the thermal load placed on the processor itself. The integrated graphics also now offers hardware decoding for the new HEVC/H.265 video codec as well as encoding through Intel’s Quick Sync feature.


Z170 chipset block diagram.

With this release, you can expect another slate of chipsets, designated the 100 series by Intel, with the Z170 as the flagship. The main improvement over Z97 is faster DMI 3.0 interface between the chipset and processor, a modest increase in native USB 3.0 ports, and a large surplus of PCI Express 3.0 lanes which will be primarily utilized to facilitate faster storage and interface options.

Windows 7 users should take note that EHCI (Enhanced Host Controller Interface) has been dropped, a feature required for installing the O/S from a USB key. Windows 8 and 10 support USB installation through xHCI, so there are no issues there. If you’re not ready to move on to Microsoft’s newer operating systems, a fresh install of Windows 7 must be performed from a DVD, and during the install no USB interface devices will be usable, so a PS/2 keyboard will also be required (assuming the board even offers one).


Our Core i7-6700K sample.

The Gigabyte Z170X-UD5.

The motherboard for this review, the Gigabyte Z170X-UD5 takes advantage of the added PCI-E lanes, sporting two M.2 slots, three SATA Express ports, and a USB 3.1 controller with both a 3.1 and Type-C connector at the back. Rounding out the main features of this US$190 ATX model is support for 64GB of DDR4 (running up to 3466 MHz via overclocking), three PCI-E x16 3.0 slots supporting 3-way CrossFire and 2-way SLI, and an ASMedia SATA chip bringing up the total number of SATA 6 Gbps ports from six to eight.

While the socket is new, it uses the same mounting hole spacing as the rest as previous LGA115x platforms so aftermarket heatsink compatibility is preserved.

TEST METHODOLOGY

Motherboards:

  • Gigabyte X99-UD4P – LGA2011-v3, X99 chipset, ATX
  • Gigabyte Z170X-UD5 – LGA1151, Z170 chipset, ATX
  • Gigabyte Z97MX-Gaming 5 – LGA1150, Z97 chipset, microATX
  • Asus Sabertooth 990FX R2.0 – AM3+ socket, 990FX chipset, ATX
  • ASRock FM2A88-ITX+ – FM2+ socket, A88X chipset, mini-ITX
  • Asus F2A85-M Pro – FM2 socket, A85X chipset, microATX

Common Test Components:

  • Kingston
    HyperX Genesis memory
    – 2x4GB, DDR3-1866 @ 1600 MHz, C9
  • Kingston Fury memory – 2x4GB or 4x4GB, DDR4-2667, C15
  • Seasonic
    SS-400ET
    power supply – 400W, ATX
  • Scythe Kabuto
    CPU cooler – stock fan at 800 RPM
  • Noctua NH-L12 CPU cooler – stock 120 mm fan only at 900 RPM
  • Microsoft
    Windows 7
    operating system – Ultimate, 64-bit

IGP Test Components:

  • ADATA XPG SX910 solid-state drive – 128GB, 2.5-inch, SATA 6 Gbps
  • Kingston HyperX 3K solid-state drive – 120GB, 2.5-inch, SATA 6 Gbps

CPU Test Components:

  • Asus EN9400GT Silent Edition
    graphics card – 512MB
  • Western Digital VelociRaptor
    hard drive – 300GB, 10,000RPM, 16MB cache

IGP test platform device listing.

Measurement and Analysis Tools:

Timed Benchmark Test Details:

  • Photoshop: Image manipulation using a variety of filters, a derivation
    of Driver Heaven’s Photoshop
    Benchmark V3
    (test image resized to 4500×3499).
  • NOD32: In-depth virus scan of a folder containing 32 files of varying
    size with many RAR and ZIP archives.
  • WinRAR: Archive creation with a folder containing 68 files of varying
    size (less than 50MB).
  • iTunes: Conversion of an MP3 file to AAC.
  • TMPGEnc: Encoding a XVID AVI file with VC-1.
  • HandBrake: Encoding a XVID AVI file with H.264.

Gaming Performance Benchmarks:

Video Test Suite:


1080p | 24fps | ~22 mbps

H.264/MKV: A custom 1080p H.264 encoded clip inside an Matroska container.

 


1080p | 24fps | ~2.3 mbps

Flash 1080p: The Dark Knight Rises Official Trailer #3, a YouTube HD trailer in 1080p.

Testing Procedures

Our main test procedure is a series of both CPU (timed tests of real-world applications) and GPU-centric (gaming tests and synthetics) benchmarks. System power consumption is measured during the CPU tests (an average of the first 5~15 seconds) and in various states including idle, H.264 and Flash playback and full CPU and GPU load using Prime95/CPUBurn and FurMark.

Certain services and features like Superfetch and System Restore are disabled
to prevent them from affecting our results.
We also make note if energy saving features like Cool’n’Quiet and SpeedStep
do not function properly.

Estimating DC Power

The following power efficiency figures were obtained for the
Seasonic SS-400ET used in our test system:

Seasonic SS-400ET Test Results
DC Output (W)
21.2
41.6
60.2
81.9
104.7
124.1
145.2
AC Input (W)
32.0
58.0
78.0
102.0
128.0
150.0
175.0
Efficiency
66.3%
71.7%
77.1%
80.3%
81.8%
82.8%
83.0%

This data is enough to give us a very good estimate of DC demand in our
test system. We extrapolate the DC power output from the measured AC power
input based on this data. We won’t go through the math; it’s easy enough
to figure out for yourself if you really want to.

TEST RESULTS: INTEGRATED GRAPHICS

Energy Efficiency

Running off integrated graphics, the i7-6700K is supremely efficient under light load, idling at 24W AC, matching the Kaveri-based A8-7600 APU configured in 45W mode. Flash and H.264 playback is also the thriftiest we’ve seen from a socketed desktop chip. The advantage over the i7-4770K is 5~6W across the board so it appears Skylake is a big improvement over Haswell in this regard.

Under heavy load, the i7-6700K saves even more compared to the i7-4700K, about 8W during more demanding tasks. The 6700K also consumes less power than 88W Core i5/i7 Haswell parts and the 65W A8-7600. On a side note, no combination of CPU & GPU intensive tasks could push the power draw past 116W AC, so the 110W drawn during Prime95 pushes the CPU close to its thermal limit.

Gaming Performance: Synthetic

3DMark11 and Heaven 3.0 place the i7-6700K’s integrated Intel HD Graphics 530 in third spot among previously tested IGPs and a low-end discrete card, the Radeon HD 6570 paired with a dual core Sandy Bridge Core i3.

Gaming Performance: Real World

Our real world gaming tests is conducted at two resolutions, 1366×768 and 1600×900 (or whatever is the closest valid resolution available), with differing levels of image quality. The results we report are for the highest resolution and detail level with which the product can deliver a reasonably good framerate (about 45 frames per second).

Real world performance of course varies from title to title, with more demanding game like Aliens vs. Predator requiring a low screen resolution and detail level to render smoothly. 900p is certainly doable in the remaining games depending on the image quality settings, though 1080p is pretty much out of the question. Except for Lost Planet 2, there’s a clear dividing line with Haswell-based Iris Pro graphics and the discrete AMD card separating themselves from the remaining integrated solutions by a significant margin.

We arrived at our overall performance figures by giving each GPU a proportional
score with each game test having an equal weighting.
The scale has been adjusted so that the Intel HD Graphics 530 chip is the reference point with
a score of 100.

Overall, Intel Graphics HD 530 offers a 22% improvement over HD 4600, achieving parity with most of AMD’s desktop APU graphics solutions, but it’s not enough to propel it into another class.

TEST RESULTS: DISCRETE GRAPHICS

The bulk of our CPU testing is conducted with a discrete graphics card (a GeForce 9400 GT) to eliminate integrated graphics as a variable, most notably with regards to power consumption. It’s also necessary to fairly compare CPUs that do not have an onboard graphics chip such as AMD FX and Haswell Extreme models.

CPU Performance

In every test except for WinRAR, the i7-6700K beats the i7-4770K by a small margin in both completion time and power consumption. While the 6700K’s base clock speed is higher (4.0 GHz vs. 3.5 GHz) it should be noted that with TurboBoost, the 4770K actually operates at 3.9 GHz during all of these tests, while the 6700K curiously never exceeds 4.0 GHz even though it obviously doesn’t hit the limit of its thermal envelope. There’s a small but definite performance improvement per clock cycle.

The 6700K plays second fiddle to the lower-clocked i7-5960X in only two tests. Haswell-E’s quad channel memory helps it score a victory in WinRAR, which is very dependent on the memory subsystem, and having six cores aids its win in HandBrake.

Energy Efficiency

Using discrete graphics, the light load power consumption gap between Skylake and Haswell narrows considerably, suggesting that the older integrated graphics technology isn’t nearly as efficient. Under heavy load, the i7-6700K is clearly superior to the i7-4700K, drawing about the same amount of power as Core i5’s.

For users with balanced workloads, we’ve determined what we call the “average power consumption” which assumes the system is used half the time for light load activities (an average of idle and H.264 playback) and the remaining half for heavy load (an average of the power consumption used running our six benchmarks). We believe this is a very common usage pattern for an average PC — they are often left on for long periods of time, doing little to no work.

In this scenario, the i7-6700K is the king, edging out the i5-4690K by about 2W and leading the older generation i5/i7’s by 10W.

For users with heavy workloads, the total power consumed while running our benchmark suite is of pertinent interest. The total power takes into account the energy efficiency of each CPU while running our benchmark tests as well as how quickly they complete each task. This simulates the power draw of a machine that is purely for doing work and shuts down when its job is finished.

For a total workhorse system, he i7-6700K the clear-cut winner, beating out the i7-4770K by a full 2 W-hr, a 19% advantage.

CPU Performance Analysis

We arrived at our overall performance figures by giving each CPU a proportional
score in each real world benchmark with each test having an equal weighting.
The scale has been adjusted so that the popular Core i5-4690K is the reference point with
a score of 100.

With a score of 119.3, the 6700K boasts a performance increase of 19% over the 4690K and 12% over the 4770K.

To determine performance per watt, we took into account the average power consumption calculated earlier, adjusted with the 4690K as the standard with 100 points.

Given the i7-6700K’s superb performance and power consumption, it scores a tremendous 123.6 on our chart, making it a 21% improvement over the i7-4770K.

When considering the cost of a system, the CPU is only part of the equation
as the price of motherboards varies greatly from platform to platform. In the
chart above, we included the prices of the chips compared today (that are still widely available and not overpriced/obsolete due to EOL), 8GB of RAM (DDR4 for Skylake as it’s more commonly supported), and an average compatible motherboard from Newegg
that fulfill a basic set of criteria (in stock retail models, ASRock/Asus/Intel/Gigabyte/MSI
branded, microATX/ATX form factor, SATA 6 Gbps and USB 3.0 support in some form, and reasonable pricing i.e. the most extravagantly priced models are omitted).

While the 6700K is only US$30 more expensive than the 4770K, an average LGA1151 motherboard cost and extra US$37, while DDR4 memory is an additional US$20, bringing the total difference to US$92. Also keep in mind that the 4770K is an outdated model that has been usurped by the higher clocked but lower priced i7-4790K, which was released along with the i5-4690K as part of the Haswell Refresh update last year.

To calculate performance per dollar, we divided the overall performance score by the platform costs and re-scaled it, again with the i5-4670K as our reference point. We don’t have test data on the i7-4790K, but it’s significant enough to place on the chart with an estimated 10% performance improvement over the i7-4770K.

New generations of Intel CPUs typically don’t offer as much bang for your buck upon initial release and this stays true with Skylake. Based on horsepower and cost alone, the Haswell “K” chips offer more than 20% better value than the i7-6700K. Even the FX-8350 is stronger in this regard as its platform cost is almost half that of the i7-6700K. Of course Skylake does have some inherent advantages in terms of features, especially compared to AMD’s AM3+ platform, but these unfortunately can’t be assigned a dollar value.

FINAL THOUGHTS

Without any serious pressure from AMD at the high-end, Intel has continued its progression of minor improvements to their microarchitecture. However, of the past few generations, this is the most significant update since Sandy Bridge. CPU performance has received a decent bump in the area of 10% per clock cycle, which doesn’t sound significant but is a bigger boost than we saw with either Ivy Bridge or Haswell. Though less important, the top non-Iris integrated graphics tier is faster than its predecessor by more than 20%. It’s in the same league as most of AMD’s APUs but HD Graphics 530 is still only a replacement for entry level discrete graphics. Power consumption has decreased once again as the 6700K is supremely efficient when tasked with heavy workloads.

For users running a Core i5/i7 Haswell or Ivy Bridge system, the temptation to jump onto the new platform is probably just starting to stir, ardent enthusiasts excluded. If you’re on Sandy Bridge, there’s enough justification to upgrade, especially considering all the extra features that have developed over the past four years. Even if your current level of performance is satisfactory, the prospect of USB 3.1/Type-C, M.2/SATA Express, and the launch of Windows 10 adds extra pressure to start fresh. Just keep in mind it won’t be a cheap upgrade path as it requires not only a new motherboard but probably pricier DDR4 memory as well. If cost is a concern, the i5 model likely delivers much of the same performance for US$110 less.

Our thanks to Intel , Gigabyte, and Kingston for the Intel Core i7-6700K, Gigabyte Z170X-UD5, and Kingston Fury DDR4 memory used in this review.


The Intel Core i7-6700K is recommended by SPCR

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Articles of Related Interest
AMD Kabini: Athlon 5350 Desktop SoC
AMD A8-7600 Kaveri APU
AMD A10-6800K & A10-6700 Richland APUs
Intel Core i7-4770K Haswell Processor
AMD FX-8350 CPU: Piledriver Arrives

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