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.
"NOTE: This answer was written 8 years ago. Parallel programming has since become more relevant. This is likely due to inherent clock speed limits and the fast approaching transistor size limits.
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."
To me, it looks more or less like the hardware designers have run out of ideas, and that they’re trying to pass the blame for the future demise of Moore’s Law to the software writers by giving us machines that work faster only on a few key benchmarks! I won’t be surprised at all if the whole multithreading idea turns out to be a flop, worse than the ""Itanium"" approach that was supposed to be so terrific—until it turned out that the wished-for compilers were basically impossible to write. Let me put it this way: During the past 50 years, I’ve written well over a thousand programs, many of which have substantial size. I can’t think of even five of those programs that would have been enhanced noticeably by parallelism or multithreading. Surely, for example, multiple processors are no help to TeX.
For some applications, it's very easy to take advantage of multiple cores. But some other applications will never benefit from them, while the others might benefit if the developers optimize them (which is very difficult)."
It depends. If you're doing things that will use every core heavily 4 cores is better (video editing, rendering etc). Most people will find two fast cores better at the moment because not many applications are written to take full use of 4 cores
"Note that the latest i7 processors can actually increase the clock-speed on the active cores when not all of them are needed; for example, if you have a quad-core at 2.4GHz, but the software only needs 2 cores to run, then it may automatically get clocked up to 2.8GHz (not an actual figure, just an example).
And the latest generation of the i7 I think can clock up 3 or 4 bins if only one or two cores are needed. As such, it may not end up staying as much of a trade-off as it currently is..."
It all boils down to the TDP of the chip, or its Thermal Design Point. The more TDP constrained a platform is, the more you stand to gain from Intel’s Turbo mode. Let me put it another way; in order to fit four cores into a 130W TDP, each core has to run at a lower clock speed than if we only had one core at that same TDP.
At higher TDPs, there’s usually enough thermal headroom to run the individual cores pretty high. At lower TDPs, CPU manufacturers have to make a tradeoff between the number of cores and their clock speeds - that’s where we can have some fun.
This is all in context of having to choose between cores (or threads) and core frequency."
