CPU Cores: The more the better?
2014-07
Questioner
I currently have a dual-core processor at work and a quad-core at home. I've noticed both PCs are pretty equal as far as launching applications/surfing the web.
The difference I can see is that my dual-core is 2.8GHz and my quad-core is 2.4GHz.
Is it better to have a dual-core with a fast clock speed or a quad-core with a mediocre clock speed?
Your primary problem is software not written for multi-core.
Look at Jeff Atwood's excellent article on Choosing Dual core or Quad Core.
for most software, you hit a point of diminishing returns very rapidly after two cores. In Quad-Core Desktops and Diminishing Returns, I questioned how effectively today's software can really use even four CPU cores, much less the inevitable eight and sixteen CPU cores we'll see a few years from now.
You are answered here (highlight copied from Jeff's article),
However, there were some surprises in here, such as Excel 2007, and the Lost Planet "concurrent operations" setting. It's possible software engineering will eventually advance to the point that clock speed matters less than parallelism. Or eventually it might be irrelevant, if we don't get to make the choice between faster clock speeds and more CPU cores. But in the meantime, clock speed wins most of the time. More CPU cores isn't automatically better. Typical users will be better off with the fastest possible dual-core CPU they can afford.
The issue of the Front-Side Bus (that term always amused me).
With Nehalem things change... as ArsTechnica said last year.
Moore's Law has given processor designers an embarrassment of transistor riches, and nowhere is that more apparent than in Intel's 45nm Nehalem processor. Debuting in 4- and 8-core variants later this year, Nehalem packs a ton of hardware into a single processor socket. (Early numbers put the transistor count of a quad-core Nehalem at 781 million; no numbers for the 8-core model have appeared yet.) But trying to feed all of that hardware with the Intel platform's existing frontside bus architecture would be folly. So, just as importantly, Nehalem also sounds the long-overdue death knell for Intel's positively geriatric frontside bus architecture.
The radical change in Intel's system bandwidth situation that Intel's new QuickPath Interconnect (QPI) represents is perhaps the largest single factor that shaped Nehalem's design. Between QuickPath and Nehalem's integrated memory controller, a Nehalem processor will have access to an unprecedented amount of aggregate bandwidth, especially in two- and four-socket implementations.
AMD moved the memory controller into the processor earlier and used Hypertransport.
David Pearce
My Macbook has a 2.4 GHz dual core processor. Because it has two separate cores, that means it can execute two functions at once, right?
So does that mean each core is approx. 1.2GHz each (for a combined 2.4 GHz) or are they actually 2.4 GHz each, and therefore is effectively running at 4.8 GHz?
Dual (and quad) core processors confuse me.
Јοеу
Each core runs at 2.4 GHz.
Though that doesn't mean that your system is twice as fast as a 2.4 GHz single-core system. Parallelism has (in principle) at most a linear speedup but in reality it's often much slower (though still faster than a single core).
John Gietzen
To be perfectly clear, having multiple cores does NOT speed up any one program unless it was specifically designed for multi-threading.
The effect of having multiple cores is:
Each thread runs at most as fast as your core clock speed. And, parallel processing allows an application to run more than one thread at once.
This means that at most, your processing power will be double, but not on any one thread.
hanleyp
Johannes above is correct when talking about the max frequency for each core in a multi-core procesor. The frequency rating relates to each core. So, a 2.4GHz multi-core processor typically runs each processor at the 2.4 GHz max frequency. There are two exceptions (one very common and one new):
- A processor's frequency can be dynamically scaled based upon the required performance and power draw to save power when power is not needed or to lower temperature (P-State).
- Also, recent processors have a "Turbo" feature where one core runs faster than rated when other cores are not being used (Turbo Boost).
ChrisInEdmonton
Your question is about Core 2 CPUs, not Core i7. Note, though, that if you buy a Core i7 920, you will see that the CPU is a quad core processor running at 2.66 GHz. That means that each core runs at 2.66 GHz. However, due to the Core i7's Turbo Boost, the CPU may actually run at 2.8 GHz, particularly if you are running single-threaded applications.
As others have pointed out, you can't multiply the CPU's speed with the number of cores to determine how 'fast' it is, I'm just pointing out that things are actually even more confusing than that with the current generation of Intel CPUs.