2.0 GHz Intel Quad core i7 vs. 3.7 GHz Intel Duo Core i7 Processor: Why not make the Quad Core 3.7GHz?

Question

I don't really understand processors, but is the 2.0GHz Quad Core i7 really a better processor in terms of performance? If it has 4 cores why not give it greater processing speed like 2.7 or 3.0 GHz?
I am asking because I am thinking about getting the high end Mac Mini, but I see that it's processor runs at 2.0GHz and the others in the line run at 2.5 and 2.7 respectively. Why is this?

Answer 1

I'm really oversimplifying here, but...
Let's just assume that each core runs at full speed all the time, the total performance of that processor would be the sum of the running totals of each core:
Duo Core i7 = 2 (cores) * 2.7 GHZ = 5.4 Ghz total processor power
Quad Core i5 = 4 (cores) * 2.0 GHZ = 8.0 Ghz
Like I said, oversimplified.  But, you get the point.  Not to mention, most apps still aren't optimized, so at a given time they only use a single core anyway. In this case, it'd be more beneficial to have more cores, since they would (hypothetically) be able to run more simultaneous processes (four vs. two in your case).
I gues the greater question is: what were you planning on using the mini for?  Most CPUs go underutilized anyway, so you may be better off getting a 2.0, and maxing out your RAM and maybe adding a SSD.  Those upgrades (the SSD especially) will result in a very noticeable increase in performance.