I7 875k overclock: Intel’s Core i5-655K & Core i7-875K: Overclocked and Analyzed

Intel Core i7-875K Review | bit-tech.net

Results Analysis

All three of our test CPUs flew through our tests, especially when overclocked, but there were some significant differences in specific applications.

The 6-core X6 1090T BE fared well in heavily multi-threaded tests, as at stock speeds it was the fastest CPU of the three in WPrime and only fractionally slower than the i7-875K, which sat at the top of the pile in Cinebench. We were expecting this though, as the brute force of the Phenom II X6-series always delivers good performance in these tests.

The i7-875K beat the i7-930 in both these tests. This is due not only to the fact that the i7-875K has a nominal 126MHz frequency advantage over the i7-930, but its Turbo Boost technology also works better and can automatically overclock the CPU further in most cases.

Our test games gave the i7-875K a chance to shine, with the higher, and Turbo Boosted, clock speed making it the fastest CPU on test at stock speeds in Crysis, though only by 1fps. This lead grew slightly in our X3: Terran Conflict, with the average frame rate of the i7-875K 10 fps higher than the i7-930.

The i7-875K sits in that uncomfortable position at the top of the LGA1156 hierarchy. Click to enlarge.

The superiority of the LGA1366 setup soon showed though, and its triple-channel memory gave it the edge in our Media Benchmarks — the i7-930 scored 1,674 overall compared to the 1,662 of the i7-875K and the 1,367 of the X6 1090T BE.

Overclocked Performance Analysis

As we mentioned earlier, we managed to overclock the i7-875K to 4.2GHz, which represents a healthy 1.2GHz improvement over stock speeds. We were also able to overclock the i7-930 from 2.8GHz to 4.3GHz, and the X6 1090T BE from 3.2GHz to 3.87GHz. These overclocks boosted performance significantly.

At 4.2GHz, the i7-875 tore through our tests. It pulled ahead of the 1090T in both WPrime and Cinebench, but was beaten by the incredibly overclockable i7-930. This result very much set the tone for the rest of our tests; the i7-930 achieved the best scores, with the i7-875K taking second place and the 1090T BE trailing in third.

The only test in which this trend was reversed was in Crysis, where the i7-875 outperformed the i7-930 by 4fps, which is a fair margin.

Order was resumed in our Media Benchmarks though, where the i7-875K returned a respectable score of 2,124 — a significant 28 per cent increase on its stock results. Respectable doesn’t cut it with the i7-930 though, and its epic overall score of 2,328 is bordering on the obscene; represents an awesome 39 per cent improvement over its stock-speed result.

Our trusty test Titan Fenrir did the business again, and allowed us to apply a 1.2GHz overclock to the i7-875K. Click to enlarge.


We’re uncertain as to why Intel has released the Core i5-655K and Core i7-875K. Its chips are already incredibly overclockable and unlocking the multiplier does little to change this, while also potentially eroding its Extreme Edition brand.

By using the multiplier of a CPU to overclock it, you reduce the strain of an overclock on the motherboard, but you’ll still need to apply extra CPU voltage, meaning that you can’t take the cheap option in your choice of motherboard even when overclocking via the multiplier.

The nail in the coffin for the i7-875K is that it’s more expensive than the i7-930, even though it uses the inferior LGA1156 packaging. The i7-875K is very quick, but an i7-930 system is more prestigious and better value for money

If you want a high-performance CPU that costs more than £200, and you’re not scared of overclocking, the i7-930 is the best CPU. As a bonus, you can spend the money you save on the CPU on an LGA1366 motherboard and 6GB of memory.

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Score Guide

1 — Intel Core i7-875K Overclocking2 — Core i7-875K Test Setup3 — Core i7-875K Cinebench and WPrime4 — Core i7-875K Image Editing and Video Encoding5 — Core i7-875K Multi-tasking and Overall Score6 — Core i7-875K Gaming Performance7 — Core i7-875K Power Consumption8 — Core i7-875K Conclusion

Intel Core i7-875K Review | bit-tech.


Intel Core i7-875K Review

UK price (as reviewed):£282.20 (inc VAT)
US price (as reviewed):$329.99 (ex tax)

Last week we reviewed the Intel Core i5-655K, which was one of two multiplier-unlocked CPUs recently released by Intel. Today we’re focusing on its bigger brother — the LGA1156 Intel Core i7-875K.

As with the i5-655K, the i7-875K is very closely related to one of Intel’s current CPUs, namely the Core i7-870.

The i7-875K shares the same stock speed of 2.93GHz (with a max turbo frequency of 3.6GHz) and the same 8MB of L3 cache as the old i7-870. The two processors also support Hyper-Threading, meaning that Windows sees the chips as having a mighty eight execution threads, though four of these are only logical cores created from the spare resources of the four physical cores.

In actual fact the only physical difference between the two CPUs is the i7-875K’s unlocked multiplier which, as we covered in the i5-655K review, allows an extra degree of freedom when overclocking the CPU. This can be an advantage if you’ve reached the Base Clock limit of your motherboard, as you can then turn to the multiplier to push the CPU further.

The i7-875K (centre) is smaller than the LGA1366 i7-930 (right) but bigger than an old LGA775 Core 2 chip (left). Click to enlarge.

Having said this, a decent LGA1156 motherboard should be able to run with a Base Clock of 200MHz, which should be able to push most Core i-series CPUs to their limit due to their high multipliers. We certainly found this with the i5-655K, and can’t help feeling that the story could be the same with the i7-875K too.

We also prefer to use the Base Clock rather than the CPU multiplier when overclocking CPUs. Increasing the Base Clock increases the amount of bandwidth between the CPU and the rest of the system, yielding greater performance for the same overall CPU frequency.

The unlocked multiplier can be a useful feature though, and, as a result the i7-875K costs a slight premium over the i7-870 tha… wha?… wait… but… eh? Observant readers may already have noticed, but the i7-875K is actually considerably cheaper than the i7-870, which it is technically superior to. Its not even a slight difference either, as there is a clear £130 between the £282 i7-875K and the £413 i7-870

This has the effect of making the i7-875K look like a bargain, but in reality it’s more true to say that the i7-870 is incredibly bad value for money. We find it hard to understand why the LGA1156 Core i7 range even exists, as a low-end LGA1366 processor will usually provide more performance for less cash, and this CPU (especially in light of its price) sheds no light on Intel’s rationale. At £282, the i7-875K is pitched squarely at AMD’s flagship Phenom II X6 1090T Black Edition CPU, which costs £233, and the excellent i7-930, which is a little cheaper at £228.

The two K series chips both have unlocked multipliers. Click to enlarge.


Again, we wanted to find out whether or not the fully unlocked multiplier of the i7-875K would give us more overclocking potential, but we came up against the same problem as with the i5-655K. The i7-875K isn’t overclockable enough for an unlocked multiplier to be of any use.

We hit the 4.2GHz maximum of the chip by leaving the stock multiplier at 22x and bumping up the Base Clock to 191MHz, which is well below the limits of our motherboard. To do this, we used a vcore of 1.35V, a QPI/VTT of 1.2V and a CPU PLL of 1.9V. We also needed to change the memory strap to 8x to ensure that our memory ran at 1,600MHz.

Having said this the 22x multiplier of the i7-875K is lower than the 25x multiplier of the i5-655K, meaning you’re likely to reach the Base Clock limit of your motherboard sooner with the i7-875K than with the i5-655K. This is especially true if you’re planning to use water- or phase-change-cooling.

If you’re not using exotic cooling (and why would you on what is, after all, a mid-range CPU) then the default multiplier of 22x and the 220MHz maximum Base Clock that the best LGA1156 boards are capable of gives you a maximum potential overclock of 4.84GHz before having to touch the multiplier. This is a huge overclock that only the best overclockers and sub-zero cooling systems will achieve.


  • Frequency: 2.93GHz
  • Core: Lynnfield
  • Manufacturing process: 45nm
  • Number of cores: 4 x physical, 4 x Logical
  • Cache: L1: 32KB + 32KB (each core), L2: 256KB (each core), L3: 8MB (shared)
  • Packaging: LGA1156
  • Thermal Design Power (TDP): 95W
  • Features: SSE, SSE2, SSE3, SSSE3, SSE4, EM64T, EIST, Execute Disable Bit, VT

1 — Intel Core i7-875K Overclocking2 — Core i7-875K Test Setup3 — Core i7-875K Cinebench and WPrime4 — Core i7-875K Image Editing and Video Encoding5 — Core i7-875K Multi-tasking and Overall Score6 — Core i7-875K Gaming Performance7 — Core i7-875K Power Consumption8 — Core i7-875K Conclusion

Intel Core i5 655K and Intel Core i7 875K — unlimited overclocking from Intel
Odnokrylov Vladimir


A few years ago, Intel had a negative attitude towards overclocking, considering it a temporary phenomenon and almost an attempt by some dealers to get rid of stale goods. But as time went on, the Extreme Edition line was formed, which announced itself with an unlocked multiplier. And the new solutions from Intel with the «K» index once again confirm that the company seriously recognizes overclocking and is starting to launch specialized products for the middle price range. 9Ol000 Test Bench

  • Testing Intel Core i5 655K and 875K
  • Intel Core i5 655K and Intel Core i7 875K | Conclusions
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  • Today, the Core i7 / i5 families from Intel often outperform competing models from AMD, but are usually quite expensive for the price. Until now, the ultra-performance Intel Extreme Edition series was available only in a set of top models (for example, the recently reviewed Intel Core i7 980X Extreme Edition), but after the release of inexpensive Pentium E6500K processors with an unlocked multiplier, the situation changed — Intel models appeared Core i5 655K and Intel Core i7 875K, which we will now consider in detail.

    Test samples arrived in a plastic case.

    • Processor Intel Core i5 655K .

    • Processor Intel Core i7 875K .

    However, there will be no standard cooling system in the usual kit — the operating mode of the processor for overclocking is very unpredictable and the choice of CO falls on the user’s conscience. An ardent enthusiast, most likely, will take liquid nitrogen cooling, but for tests we limited ourselves to air.

    As you know, the third-level cache in Intel processors is available for any core in the processor. And this means that even in applications that do not support two or three or more cores, performance will increase somewhat in many cases.

    Program CPU-Z defined processors as follows.

    Other specifications are as follows.


    Intel Core i7-875K

    Intel Core i5-655K

    Codename Lynnfield Clarkdale
    Number of cores/threads 4 / 8 2 / 4
    Clock frequency 2. 93 GHz 3.2 GHz
    Cache 8 MB Intel Smart Cache 4 MB Intel Smart Cache
    Multiplier 22 24
    Instruction set 64-bit
    Extended set SSE4.2
    Process 45 nm 32 nm
    Heat pack 95 W 73W
    Voltage 0. 65 – 1.40 V
    Memory type DDR3-1066/1333
    Maximum temperature 72.7°C 72.6°C
    Size 37.5 x 37.5 mm 37.5 x 37.5 mm
    Crystal area 296 mm 2 81 mm 2
    transistors 774 million 382 million
    Slot LGA1156
    Intel Turbo Boost yes
    Intel Hyper-Threading yes
    Intel Virtualization for Directed I/O no
    Intel Trusted Execution no
    AES New Instructions no yes
    Intel 64 yes
    Idle States yes
    Enhanced Intel SpeedStep yes
    Intel Demand Based Switching no
    Thermal Monitoring no
    Execute Disable Bit yes

    Place of models in the lineup #

    We have already discussed the technical characteristics of the chips. But what is the position of each of the considered processors in the model range? If we consider the price range, then Intel Core i5 655K will cost the buyer $216, while almost the same model, but with the usual multiplier — Intel Core i5 650 — only $176.

    But Intel Core i7 875K is a more expensive model — it will cost $342, while the usual Core i7 870 costs about $294. So, on average, an unlocked multiplier will cost the buyer about $40-50 more than the cost of a «locked» model in the i7 family and in the i5 line. However, if we take into account the result of overclocking (more on that later), then the investment pays off.

    Note that the processors in question differ from their counterparts not only in multiplier and price — in these models we will not find support for Intel Virtualization for Directed I / O (VT-d) and Intel Trusted Execution .

    Turboboost #

    This technology, as you know, is designed to automatically increase the clock frequency, or «self-overclocking», of the processor, if the application load is significant, but not distributed to all cores. The frequency increase is performed according to the multiplier step algorithm of 133 MHz (base frequency) — on one core up to two steps, on two or more cores — only one step. We see this phenomenon in the CPU-Z screenshots.

    We carried out tests on the following stand.

    Taking into account that there was no cooling system in the kit, we took the cooler GlacialTech UFO V51 .

    Despite its rather impressive size, it neatly fit between the motherboard heatsinks, memory slots and video card and practically did not interfere.

    The testing itself was carried out in synthetic tests — both in purely computational tests and those simulating real work on a computer. The methodology was as follows — the measurements were carried out in three attempts, then the average value was determined, which is presented below in modes without overclocking, in mode Turboboost and when overclocking the processor by simply raising the multiplier.

    The following can be said about the overclocking potential with air cooling of these processor models — at our test bench we were able to achieve stable operation at a multiplier of 31 (a step by a multiplier of 32 causes errors in operation) with a base 24 for Intel Core i5 655K and at a multiplier of 30 with a base of 22, the has an Intel Core i7 875K . The maximum stable result was a frequency of 4.12 GHz per core for Intel Core i5 655K and 4 GHz per compute core for Intel Core i7 875K .

    Note also that the Intel Core i5 655K can achieve similar results (4.2 GHz) with the following performance (see screenshot below). However, such an increase in the reference frequency can potentially lead to system instability.

    We will talk about how much the performance has increased during the tests. We also made a comparison with our previous «unblocked» guest — Intel Core i7 980X Extreme Edition . You can read his review in another article, and we proceed to the tests.

    Fritz Chess Benchmark 4.2 lined up the processors according to their price and power, however, nothing else was expected — in the first place is Intel Core i7 980X Extreme Edition , followed by Intel Core i7 875K , and closes Intel Core i5 655K .

    The greatest gain, of course, we get in overclocking, and mode Turboboost only slightly exceeds the standard result of processors.

    In the test involving 8 threads Intel Core i5 655K could not take part — there are only 4 of them.

    But in wPrime 2.0 Turboboost , but it is still far from the top model of the line even with overclocking, although the difference is less compared to Intel Core i5 655K .

    In SiSoftware Sandra 2010, the alignment of forces has not changed, but in general we can say that the difference in computing power in all modes between the presented models is 30-40%.

    The expected result in tests for multi-core performance — data exchange directly depended on overclocking, but it is interesting that inside the processor the throughput efficiency of even the younger model was at the level of the top one, but Intel Core i7 875K showed the worst result in this regard.

    In the first two tests in Everest version 5.50.2127 , the situation is as follows — the efficiency of Turboboost is low, but overclocking gives very good results. The balance of power is unchanged.

    But the decryption test CPU AES showed a very unexpected result — Intel Core i7 875K showed only some 10-12% of even Intel Core i5 655K , not to mention Intel Core i7 980X. The reason is the lack of support for the instruction set AES New Instructions in the processor itself, which led to this result.

    In tests of floating point operations, the balance of forces exactly repeats the previous distribution. In further tests, the situation is absolutely similar, so we will comment only on indicators that differ from this.

    The single-processor test CINEBENCH R10 is more dependent on the clock frequency, so the result of the Intel Core i7 875K is lower here.

    However, the multi-threaded test puts everything in its place.

    Single-threaded 7-zip tests also show that the junior model is only slightly inferior to the older line in operations where clock speed is important.

    Tests in WinRAR show about the same results as other benchmarks with the correct use of processor resources — both the total L3 cache and clock speed. The distribution of models by performance corresponds to the price ranges of the presented models.

    The last test we did was in the Paint.NET editor. Note that the difference between the standard mode and the Turboboost mode is much smaller for the older model — most likely this is due to the large number of simultaneously involved threads — 12 versus 8 and 4 for Intel Core i5 655K and Intel Core i7 875K respectively.

    In conclusion, with a more powerful cooling system, fine tuning of the supply voltage and additional overclocking using the reference frequency, the processors Intel Core i5 655K and i7 875K will also have higher frequencies available. And the main advantage (overclocking using a multiplier) makes these processors a very useful acquisition for a novice overclocker, allowing you to significantly overclock the system in just a few minutes.

    There are no obvious flaws in the models, except that some technologies are missing, but this does not mean much for these products. After all, the focus of both processors is very narrow — the overclocking sector, and they usually overclock for everyday tasks. As for the «added» cost, it is acceptable — even our results with air cooling are quite good and, perhaps, worth the overpayment.

    If Intel releases models with an index of K for the Core i3 line, it will greatly oust the positions of AMD Black Edition processors in the lower price range.

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