How do I compare CPUs? Dual Core, Core 2 Duo, Quad Core...

[706]

This is a very newbie question but it seems like a while ago I could compare CPUs based on how many ghz they had. These days I'm really lost with trying to choose a nice CPU. I personally prefer Pentium to AMD but I'm not sure how to compare which ones are better than others.

As an example I'll use a few of the computers on the dell website. I have a 3.0ghz P4, if I was to buy one of the dell computers I could get a Core 2 Duo 2.3ghz or 2.6ghz. Now technically mine has more ghz, but as its Core 2 Duo does that mean it has 2 cores each at 2.3 or 2.6, therefore they would have 4.6 and 5.2ghz? Or is 2.3 and 2.6 still their actual ghz but they make use of it better than my old P4 would and therefore be better?

Or if I wanted to I could get a Quad Core at 2.4ghz. Does this mean it has 4 cores each at 2.4ghz, for a total of 9.6ghz? Is that how you can compare the types of CPUs, that a Core 2 Duo has twice the ghz it shows, and a Quad Core has 4 times, or is there some other way in which a Quad Core at 2.4ghz would be better than my 3.0ghz? How can I compare them to determine which would be better?

[Toryn]

The way I understand the new cores working. is that say you ran a programme that needed 2.4ghz of processing power and another that needed a further 2.4gz (purely random numbers just for an example)

On the P4 3gz both programmes would have to be ran on one core, slowing the speed each programme works at. Where as on the dual and quad cores, one programme would be assigned to core1 and the other core2 resulting in no performance decrease.