choice of a mean overclocker / processors and memory


Our first acquaintance with the processors of the Kaby Lake family took place more than a month ago. Then we tested the flagship model in the lineup and came to the conclusion that Intel decided to offer almost the same thing as before (see Skylake), but with an optimized “supply-frequency” curve. In other words, there are no differences in the microarchitecture among the new processors, but there is an improved production technology of 14+ nm, which allows to obtain semiconductor crystals with better energy efficiency and increased frequency potential. It is thanks to this that the updated Core series has some sense. The processors included in it received higher performance, remaining within the usual thermal packages. In our initial review, we talked about this with reference to a representative of the Core i7 class. But in fact, similar acceleration affected all the models of the seventh generation Core. And today we will look at what Intel can now offer to consumers in a more down-to-earth price segment, to which the LGA1151 processors of the Core i5 class belong. As with Core i7, this class has its own fresh overclocker model, Core i5-7600K, and it was she who became the main character of the second review of Kaby Lake on 3DNews.

Historically desktop processors Core i5 – one of the most discussed products of the company Intel. The fact is that the differences Core i5 from Core i7 are not so obvious. Everything revolves around the fact that the younger family does not support Hyper-Threading, but at the same time, like the older one, it still has four processing cores. Formally, this can cause a rather serious difference in performance, but in fact it appears only in a few cases – in those applications that can create more than four peer-to-peer streams. As practice shows, there are not so many applications of this kind, and they mainly concern professional tools for creating or processing digital content. In most of the tasks that are solved by the average users, including games, there is practically no sense from Hyper-Threading. The price of Core i5 processors is much lower compared to Core i7. For example, the same Core i5-7600K is cheaper than the Core i7-7700K, almost by $ 100, which can be successfully used to buy a more powerful graphics card, more memory or SSD-drive. Therefore, Core i5 processors may well seem to be a much more rational basis for the LGA1151 platform.

Until recently, that’s exactly what it was: the older Core i5 traditionally acted as one of the best options for a gaming computer in terms of price and performance. However, with the release of the latest generations of Intel processors slightly tweaked the characteristics of older representatives in the series of Core i7 and Core i5, and now to give preference to the Core i7 makes sense not only to the notorious maximalists. The fact is that, starting around mid-2014, when the Devil’s Canyon line came on the market, the representatives of the Core i7 series acquired an additional plus: their nominal frequencies compared to the Core i5 became noticeably higher. This situation is still present: the gap in the operating frequencies of older Core i7 and Core i5 is about 300 MHz, which is actually not so small.

Of course, it can be argued that the older Core i7 and Core i5 are a CPU with unlocked multipliers that are very easy to overclock, and therefore superiority in nominal frequencies is only an imaginary advantage. But practice shows that not everything is so simple. Core i7 for some reason and overclocked better than their younger brethren, although the logic should be the other way around. Indeed, Core i5 does not support Hyper-Threading technology, so at the same frequency they should allocate less heat and, therefore, should easily conquer more distant frequency boundaries. However, in fact it turns out that the Core i7 in the overclock can work at an average frequency of 100 MHz higher than that of the similar Core i5 – this is evidenced by our experience and statistics collected on overclocker forums. What’s the matter, it’s hard to say with full confidence, but it’s very likely that Intel for the older family deliberately chooses more successful semiconductor crystals.

It turns out that the microprocessor giant is trying hard to reorient the Core i5 in such a way as if it were a compromise proposal for those who can not afford a full Core i7. How true is this attitude and is it true that modern Core i5 from the Kaby Lake generation can no longer be considered a full replacement for the Core i7? In this review, we will try to answer this question reasonably.

⇡ # Core i5-7600K in details

The older model in the updated line of LGA1151 processors Core i5, which came design Kaby Lake, – overclocker CPU with unlocked multipliers. But this modification, called the Core i5-7600K, differs from other Core i5 of the new generation, not only this. It also has higher clock speeds than its counterparts and outperforms the “regular” Core i5-7600 by a weighty 300 MHz. However, this advantage is reflected in the heat release. Core i5-7600K is the only representative in the Core i5 series, which is assigned to a 91W thermal package. Yet the rest of the CPUs in this class fit into either a 65-watt thermal package, or, in the case of energy-efficient T-series processors, 35 watt.

The frequency response of the Core i5-7600K is better than its predecessor from the Skylake generation. The nominal frequencies of the Core i5-6600K were in the range 3.5-3.9 GHz (depending on the load). The novelty is 300 MHz faster: its nominal frequency is set at 3.8 GHz, and in turbo mode this processor can accelerate to 4.2 GHz. The clock speed was improved by the improved 14+ nm process technology that Intel developed within the new “process-architecture-optimization” strategy, which replaced the “tick-to-do” principle at least until the company came to use in the production process of EUV lithography (with ultra-high ultraviolet radiation). Optimization in the structure of 14-nm transistors (widening the gaps between the gates and increasing the height of the edges of the channels), performed without introducing changes in the resolution of the technological process, opened up an additional frequency potential. And in Core i5-7600K, as well as in Core i7-7700K, it went into action.

The screenshot of the diagnostic utility CPU-Z shows that the typical Core i5-7600K frequency on which this processor is running at full load on all the cores is 4.0 GHz. In the case if the load is of a single-threaded nature, autotyping to 4.2 GHz, determined by Turbo Boost 2.0 technology, is triggered. Please note, the VID (nominal voltage) of our test processor is set at 1,215V, and this allows us to say that the frequency increase in the Kaby Lake family occurred without any increase in energy appetites. In other words, we are really dealing with the optimization of design, and not with the banal factory overclocking of Skylake.

Nevertheless, most of the characteristics of Core i5-7600K coincide with those of Core i5-6600K. As before, we have a quad-core processor with disconnected Hyper-Threading technology and with a reduced to 3MB cache of the third level. With this in mind, it’s no surprise that the Kaby Lake family of processors is fully compatible with any LGA1151 platform options – for older motherboards based on the 100th series of logic chips, only the BIOS update is required. Even the official price of the Core i5-7600K is set at the same $ 242 as for its predecessor. And this means that today it does not make any sense to buy Core i5-6600K, because Core i5-7600K offers more performance for the same money.

The maximum frequency in turbo mode, GHz

Core i5-7 600K Core i5-6600K ]
The code name

Kaby Lake

Skylake

The time of the announcement

Q1, 2017

Q3, 2015

Nuclei / flows

4/4

4/4

The technology of Hyper-Threading

No

No

Base frequency, GHz

3.8

3,5

4.2

3.9

The unlocked multiplier

There are

There are

TDP, W

91

91

HD Graphics

630

530

The frequency of the graphic core, MHz

1150

1150

L3-cache, Mbyte

6

6

Support for DDR4, MHz

2400

2133

Support for DDR3L, MHz

1600

1600

Technologies vPro / VT-d / TXT

Only VT-d

Only VT-d

Extensions of the instruction set

AVX 2.0

AVX 2.0

The packaging

LGA1151

LGA1151

The price is

$ 242

$ 242

Like all other CPUs with the suffix K in the name, the Core i5-7600K is a fully overclocked processor. On motherboards based on sets of logic Z170 and Z270, its frequency can be increased above the passport values ​​both by changing the multiplying factor, and by increasing the frequency of BCLK. In this respect, the Core i5-7600K is also similar to the Core i5-6600K. But do not think that in all, in addition to the clock frequency, the Core i5-7600K is similar to the related processor of the generation Skylake.

First, for the Core i5-7600K, compatibility with DDR4-2400 SDRAM, which was not mentioned before, was declared. This means that Intel has slightly “pulled up” the characteristics of the memory controller built into the processor, which in practice can be expressed in the smoother operation of overclocking DDR4 memory modules at high frequencies. For example, the world record for overclocking DDR4 SDRAM to the frequency of 5260 MHz is installed with the processor of the Kaby Lake family.

Secondly, the Core i5-7600K, like all other Kaby Lake, has a slightly different frequency of the built-in north bridge compared to the Skylake processors. With respect to the CPU under consideration, it is 3.8 GHz, while the nominal frequency of the north bridge Core i5-6600K was synchronized with the frequency of the processor cores. This feature, in particular, explains the fact that in complex complex tests conducted at acceleration to the same frequency, Kaby Lake slightly lags behind its predecessors, despite the fact that there are no differences in the microarchitecture between them.

And thirdly, the Core i5-7600K has a newer integrated graphics core Intel HD Graphics 630. However, in the 3D part it completely corresponds to the past core of the HD Graphics 530: it is exactly the same graphics level of the GT2 with 24 actuators and a frequency of 1.15 GHz. The growth of the index in the name of the GPU is due exclusively to new multimedia features aimed at hardware acceleration of processing 4K-video. Details can be found in the review Core i7-7700K but the main features are the appeared support for decoding H.265 Main10 and VP9 in the resolution of 2160p, and also support for encoding in the format VP9.

⇡ # Dispersal

Our overclocking story Core i5-7600K is a complete disappointment. The first tests of representatives of the Kaby Lake family became a source of very bold expectations: still, those samples that the microprocessor giant distributed to reviewers for surveys easily took unthinkable for processors of past generations boundaries. For example, a sample of the Core i7-7700K that got into our laboratory worked without problems at 4.8 GHz, and some of our colleagues managed to conquer a psychologically important five-hugger line. But the test copy of Core i5-7600K, which was bought by us in a regular retail store, could not even come close to the desired level of 5.0 GHz. And this, it seems, is not an accident. Even at the time of Devil’s Canyon and Skylake, we began to notice that processors with disconnected Hyper-Threading technology are not accelerating at all better than the colleagues from the Core i7 family. With the release of Kaby Lake, this pattern only worsened. Therefore, if you want to get the maximum frequency, it’s better to immediately focus on the more expensive Core i7-7700K. For Core i5-7600K, judging by everything, Intel uses the worst in frequency properties semiconductor crystals. In addition, it is very likely that the first lots of Kaby Lake semiconductor crystals, which went also into samples for the press, had the best frequency potential. Otherwise, it will not be easy to explain what happened.

And it happened that the test Core i5-7600K was able to accelerate only to the frequency of 4.5 GHz, that is, about the same as the most successful Core i5 processors of the Skylake generation.

To ensure stable operation in this state and error-free testing in LinX 0.7.0, the supply voltage required to be increased to 1.325 V. With a lower voltage, errors occurred. However, even with such a very moderate increase in the voltage, the temperature was stormed by the limit marks: the heating of the hottest core reached 96 degrees. It is quite obvious that there was no question of any further dispersal here.

Thus, our experience with the serial Core i5-7600K allows us at least to say that the best overclocking of Kaby Lake in comparison with Skylake is far from an immutable truth. And it is quite possible that the overclocking potential of the Core i5-7600K may be even worse than that of its predecessor.

However, the Core i5-7600K, like the Core i7-7700K, has a new feature that allows you to get out of this situation: AVX Offset. The bottom line is that the highest heat dissipation is caused by AVX-instructions, and it is their performance that leads to overheating of the computing cores. To neutralize such selective heating, Kaby Lake family processors provide the opportunity to temporarily reduce the clock frequency at the time of processing complex vector commands. This function is available through the motherboard BIOS and implemented as an additional negative multiplier, which is applied to the processor frequency in those cases when it encounters AVX instructions. As a result, by sacrificing performance in not too common applications, based on AVX-commands, the user can get better processor overclocking in other cases.

To test everything that was said in practice, we tried to fix the situation with extremely limited overclocking of the test Core i5-7600K using the “back multiplier AVX” 10x. In other words, we set up the processor in such a way that its frequency when working with AVX-commands temporarily decreased by 1000 MHz, which should allow us to get rid of overheating in the most problem-solving tasks in terms of energy. And it helped: without provoking overheating, the supply voltage turned out to be significantly higher than 1.325 V, so the limiting frequency of the test Core i5-7600K was quite expected to be moved further – up to 4.8 GHz.

Important nuance: when checking the overclocking in case of using the “reverse multiplier AVX”, there is no sense to rely on the usual modern utilities for checking the stability. All of them actively use AVX-instructions, so the processor will work in them in a weakened mode – at a reduced frequency. To take this into account, we used the old version of LinX 0.6.4: it works with SSE4, but AVX does not.

Stable operation at 4.8 GHz frequency required to increase the supply voltage to 1.4 V. The maximum heating of the processor cores in such conditions did not exceed 80 degrees. It is clear that such a mode would be completely unacceptable if AVX-commands were present in the load. But when working with them, the frequency decreased to 3.8 GHz, and therefore there were no signs of overheating. In other words, the appearance of the “back multiplier AVX” in Kaby Lake really makes it possible to get a more or less decent acceleration even in completely hopeless cases.

In general, all the difficulties with the overclocking Core i5-7600K, which we had to face, can be easily attributed to the thermal interface that Intel places between the processor chip and the copper (nickel-plated) heat-distributing cover that closes it. The area of ​​the quad-core Kaby Lake crystal with GT2 graphics is about 125 mm 2 . This is a very small surface, and efficient removal of heat from it is one of the key factors affecting the final result of overclocking. However, in the case of processors in LGA1151, Intel saves on high-quality thermal paste, and the polymer thermal interface used with the density of heat flow from the overclocked Kaby Lake is clearly not coping.

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