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I'm looking at building a computer for my brother. Back when I built my own I used a 4th-gen CPU. My thinking is "well he should obviously have the latest generation because they say they're always faster than the previous generation".

But when looking at benchmarks, I'm seeing the 4th-gen CPU that I used as cheaper and faster than the latest 6th-gen offering.

So 3 questions:

  1. Why is the benchmark slower?
  2. Is 6th-gen actually slower?
  3. Why would someone choose 6th-gen if 4th-gen is faster and cheaper?

Research: - My 4th Gen Processor: i7-4790K - Latest 6th Gen Processor offering: i7-6700K - Benchmarks: https://www.cpubenchmark.net/high_end_cpus.html

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Both the i7-4790K and the i7-6700K have very similar profiles, both have:

  • a base clock of 4GHz
  • 4 Cores / 8 Threads
  • 8MB Cache
  • Support for SSE4.1/4.2, AVX 2.0 Instruction Set Extensions

However, there are also slight differences in:

  • the system bus architecture: DMI3 @ 8GT/S (i7-6700k) vs. DMI2 @ 5 GT/s (i7-4790k)
  • Boostclock: 4.2 GHz (i7-6700k) vs 4.4 GHz(i7-4790k)
  • supported memory type: DDR4 (i7-6700k) vs. DDR3 (i7-4790k)
  • memory bandwidth: 34.1 GB/s (i7-6700k) vs. 25.6 GB/s (i7-4790k)
  • max. memory size: 64GB (i7-6700k) vs. 32GB (i7-4790k)
  • integrated GPU: Intel HD 530, DirectX 12 (i7-6700k) vs. HD 4600, DirectX 11.2 (i7-4790k)

That being said, the performance difference one can expect between those CPUs is rather low. Though both have certain advantages. The features that will make the biggest difference between those CPUs are the considerably faster memory bandwidth of the i7-6700k vs the higher boost clock of the i7-4790k. So in practice, one can expect the i7-6700k to outperform the i7-4790k where memory bandwidth is crucial, whereas the i7-4790K will have slight advantages in applications requiring high single core compute performance - single core because that is the scenario where the CPUs will reach their highest boost clock.

Now to your questions:

1. Why is the benchmark slower?

The benchmark is slower because it seems to take advantage of the i7-4790k's higher boost clock rather than the i7-6700k's higher memory bandwidth.

2. Is 6th-gen actually slower?

As I explained above, this totally depends on the application. If you look at these results, you'll see the i7-4790k outperform the i7-6700k in some applications, where it's the other way around in other applications. But the most important observation you should take away from those results is:

In practice, there is not much of a difference in speed unless you're actually in need of very high memory bandwidth and overall memory size. For most homeusers, 32GB of RAM will likely be enough though.

3. Why would someone choose 6th-gen if 4th-gen is faster and cheaper?

Someone should definitely get the i7-6700k if he needs more than 32GB of RAM or is using applications relying heavily on memory bandwidth or wants certain features that are available only on newer mainboards.

If those advantages of the i7-6700k are not of use to you and the i7-4790k is considerably cheaper, you just might want to buy the i7-4790k, you will not notice a difference.

There is one more thing to consider, if you're into overclocking. The i7-4790k draws its advantages over the i7-6700k mainly from the higher boost clock. Rumors say that Intel has improved the thermal compound between die and heatspreader of newer CPUs. If this actually results in better heat dissipation for the i7-6700k, you might achieve higher overclocking rates with the newer CPU, causing the i7-4790K to fall behind the i7-6700k in its most important advantage - the higher boost clock. Still, the differences between both CPUs will be very small to not humanly noticeable.

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    A thorough answer thanks. So my take away is it mostly comes down to using memory intensive applications...
    – Niccaman
    Sep 27, 2015 at 19:43
  • Yes that is pretty much it. If you don't plan on adding a dedicated graphics card then the above mentioned DirectX12 featureset supported by the i7-6700k's integrated HD 530 GPU might also be a nice advantage over the i7-4790k, since its HD4600 "only" supports DirectX11.2.
    – norritt
    Sep 27, 2015 at 20:20
  • I do not understand, why intel makes the new-generation processors slower than the older generation processors? Jul 17, 2016 at 0:19
  • I was surprised myself . . . I have an i5-4690 and the comparable i5-66nn processor appears to be only ≅ 5% faster based on each's Passmark score (a rating system I've found to be very realistic and very useable in the past). When you consider that to upgrade it would cost not only the price of the CPU but of a new motherboard as well (the two CPUs have different architecture) it definitely isn't worth it for me, unless I move up to i7 or Xeon, which I realistically don't need. Apr 11, 2017 at 19:16

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