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My current laptop has a Core i7-2670QM CPU which was released in October 2011:

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When I look at more recent laptops, with CPUs released this year, it's not clear which one is more powerful.

For instance the Core i7-5500U CPU released in January 2015:

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It has better graphics, a slightly higher frequency (2.4Ghz vs 2.2Ghz), but half the number of cores and less L2/L3 cache (which on a side note puzzles me as I would expect a CPU released 4 years later to be a lot more powerful).

If I want to do tasks in the browser (Gmail, Google Calendar, Youtube, Gogle Drive...), which of Core i7-2670QM or Core i7-5500U is more powerful?

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    You’re comparing totally different series of CPUs. One is a “QM” (4-core mobile) series CPU, the other a “U” (ulta-low power) series CPU. Also, hardware shopping questions are off-topic on Super User.
    – Daniel B
    Nov 17 '15 at 20:55
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    The Core i7-5500U is about 30% slower than the Core i7-2700QM. However, for tasks that cannot take advantage of multiple cores, it's about 12% faster. Nov 17 '15 at 21:12
  • To those voting to close as a shopping request: To me, OP's not asking what to buy, he's trying to get some clarification on the differences (of which he did show research effort on) so he can decide what to buy. But it's borderline for sure. ;) Nov 17 '15 at 22:06
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    @Ƭᴇcʜιᴇ007 - Where does it end? While the quality of this question I admit is high, if we accept this question, we have to accept the next question to explain the difference between Process A released in 2015 to Processor B released say in 2017. I mean honestly there are lots of sites dedicate to scoring the performance of CPUs. I mean the GPU in the i7-5500U is about 3x as powerful as the Core i7-2700QM just because its several gpu generations newer. So does that count as being more powerful?
    – Ramhound
    Nov 18 '15 at 18:42
  • @user359650 - You would see better performance with when watching YouTube videos if the only GPU you had was the HD Graphics 5500 considering the HD Graphics 3000 was considered to be complete trash by most people ( in other words bargain bin performance ).
    – Ramhound
    Nov 18 '15 at 18:46
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(which on a side note puzzles me as I would expect a CPU released 4 years later to be a lot more powerful).

You are expecting something that just isn't (currently) true. CPUs have really plateaued over the last several years, so each generation is an incremental move toward better efficiency rather than a leap forward in raw computational power and clock speed.

Also "powerful" is a subjective term, and your also comparing an ultra-low voltage dual core ("U") to a quad core for mobile ("QM"), so it's hard to know what you're expecting exactly...

What improvements have there been between generations?

To find out some basics let's consult Intel's ARK:

Major advancement - die size:

Which is a major contributor (along with only having half as many cores) for this improvement:

This lower TDP and tighter lithography lends to things like improved battery life.

Other than that, most still looks equal right?

Now consider why they changed architectures, and what new designs may add.

A non-specific, hypothetical example would be improvements in certain calculations. They can (and do) implement new features that do certain (sets of) calculations much more efficiently. So, for example, they can now do calculations X, Y, or Z in one clock cycle instead of 3, therefor tripling the performance of those calculations, all without changing clock speed, or enlarging caches, or widening memory bandwidth. If you use those certain calculations a lot, you're going to notice a massive speed improvement.

If I want to do tasks in the browser (Gmail, Google Calendar, Youtube, Gogle Drive...), which of Core i7-2670QM or Core i7-5500U is more powerful?

It will probably make little to no noticeable difference with that kind of usage.

To really know the difference, you need to do benchmarks and compare.

According to 3DMark's Benchmark comparison (higher is better):

  • 2670QM: 4750
  • 5500U: 7100

The 5500U scored a ~40% higher score, with only half as many cores, while using ~1/3 the electricity.

This tells me that the 5500U is considerably more "powerful" (at least in this one benchmark. :) ).

Once you start looking at multi-threaded benchmarks, a quad-core (that close in age and architecture) will often (if not always) outperform the dual core, for obvious reason.

At that point you should probably be looking at comparing to a 5th generation Quad Core (ie: the i7-57X0 and i7-58X0 processors @ ~45W TDP), and do further benchmarks to get a more apples-to-apples comparison.

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  • Finally someone addressed my question: "It will probably make little to no noticeable difference with that kind of usage", thanks. Everybody else is so busy showing off their knowledge about CPUs: which artchitecture, which bla bla bla... As an end user I couldn't care less: which one is the fastest for the tasks I have to perform, that's what matters to me.
    – Max
    Nov 18 '15 at 7:56
  • Let alone the fact its tough to compare a 2nd generation old Core processor to a 5th generation Core processor. While the frequency of the processor is slower, if it actually more efficient at doing an instruction, the actual speed makes less of a difference. YouTube is the only task that would see an improvement, if and only if, that was the only GPU you were using since that would then bring in hardware acceleration into the mix.
    – Ramhound
    Nov 18 '15 at 18:50
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First, understand that operating frequency isn't such a meaningful metric for comparing chips anymore, and hasn't been for more than a decade. Chips hit 3-4GHz in 2002 or so, but haven't gone up since, due to the infamous Power Wall. From there, chips improved by adding additional cores, lowering power, moving more an more previously external components into the chipset, optimizing threading models, implementing parallel pipelining, etc. Nowadays, it is often hard to look at the standard specs and tell the differance.

Second, note that Intel always has a number of differentiated product lines, so that they can fit into a set of pre-selected price points, and always have a new model at each point, so it will always be possible to find modern chips that appear to have lower metrics than chips from previous years. This is especially true if you are crossing product lines.

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@Frank's answer about not being able to know for sure reminded me (I'm getting old) that there are CPU benchmarks out there designed precisely for that purpose, and it seems my old CPU performs better:

http://www.cpubenchmark.net/common_cpus.html

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  • In my opinion, cpubenchmark.net is one of the most unreliable benchmarks out there. It seems to be quite random and doesn't give you any specific useful information such as single core performance. There are tons of better benchmarks, I'd recommend going to notebookcheck.net and look at the different ones. Which one is the best depends on your application and cpubenchmark.net rarely is more than a very rough indication.
    – BramMooij
    Nov 8 '16 at 8:45
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Please use ark.intel.com for Intel CPU comparisons. You get there when googling for the CPU, usually it's the first hit.

The main difference is that one is a M, while the other a U processor. Mobile (Laptop) vs Ultra-Low-Power (Netbook)

http://ark.intel.com/products/53469/Intel-Core-i7-2670QM-Processor-6M-Cache-up-to-3_10-GHz

TDP 45 Watts

http://ark.intel.com/products/85214/Intel-Core-i7-5500U-Processor-4M-Cache-up-to-3_00-GHz

TDP 15 Watts, therefore utlra low power. You'll find these in tablets.

Also the difference between Intel HD Graphics 3000 and 5500.

In every TDP segment you can compare how powerful CPU's are one to another, but not across different TDP segments.

This is what makes the U processors so impressive, you'll want the fastest 6.Gen 15W CPU for a 24/7 home server, but you know that a 45W CPU would be a lot faster.

Keeping this in mind, go and compare benchmarks, knowing that you are comparing two different segments.

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The i7-5500u indeed has significantly better graphics. The single core performance is slightly better than that of the i7-2670QM, but performance when all cores are running to the max is higher for the i7-2670QM.

The reason this is possible, is that the i7-5500u is from the low power 15 Watts range of intel, whereas the i7-2670QM has a TDP of 45 Watts. Judging from the benchmark results of notebookcheck.net (a good source for laptop cpu benchmarks), this i7-2670QM is about 20-30% faster when using it for very intense computational tasks. However, for the intended use you state, it shouldn't make any difference which one you use. The CPU will never be pushed to the max, and either CPU will feel just as fast. Therefore, provided you are happy with your current battery life, and have no other reasons to upgrade your laptop, I would just keep your old one. If the old one is getting slow, replacing HDD with an SSD and reinstalling windows on that will do much more for you than the CPU upgrade.

benchmark comparison list (I consider wPrime32 to be a good max usage benchmark): http://www.notebookcheck.net/Mobile-Processors-Benchmark-List.2436.0.html

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You compare different CPU classes. The QM is a quad core CPU (real 4 cores + hyper threading) and the U and M cpus are Dual Core CPUs. If you want to compare CPUs you have to compare your old CPU to the new QH models and not to Dual Core CPUs which are optimized for battery life (U) and not for CPU power.

A currently often used CPU for gaming laptops is the Intel i7 6700HQ which is a comparable CPU with more Power.

For normal work, your old CPU is still fast enough, so buying new hardware makes no sense.

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