OT: Building a new computer...

[Fyron]

Quad core desktop CPUs will be good in maybe 3-4 years. Stay far away from them for now if most of your time is not spent rendering hugely complex 3d models.

I thought dual or quad core meant 2 or 4 times the Mhz but I have gotten conflicting information that it is the speed listed but having 2 or 4 cores makes it process faster.

Not exactly. 2 cores is like having two discrete CPUs, so instructions from two processes can be executed at the same time. Each core is necessarily slower than a CPU that used the same process tech, but used the whole core. The reason why multiple CPUs/cores tend to be better than a big single one is that most processes (even games) don't really need all of instruction processing capacity of the last generation of single-core CPUs. Its better to split up the silicon so that the OS task scheduler has more leeway to manage applications (such as kernel and background processes). In theory, 4 cores are better than 2, since the system can process instructions from more processes concurrently.

When you compare a dual core to a quad core CPU, both made on the same silicon process level (45 nm now for the latest stuff, IIRC), a dual core tends to come out ahead in real world applications for home use. Each core has twice as much capacity to process instructions as a quad core CPU. On the other hand, a quad core CPU can process instructions from twice as many applications at once. There are pros and cons for each situation. When you have a ton of concurrent processes (or threads of one big one) running all the time, you want as many CPUs as possible. Servers tend to benefit greatly, as do workstations that do a ton of data crunching (or model rendering if the renderer is capable of using many CPUs). When you have just one app that is very CPU intensive, its better to have a dual core CPU.

Games don't really lend themselves to many concurrent threads. There is a lot of optimization that can be done with 2 threads, but going to 3 or 4 is usually redundant, since the extra tasks that could be split off tend to be far less process-intensive than the main threads. Plus, multi-threading in games is still nascent; most devs are still trying to wrap their heads around two concurrent threads, much less many.

In summation, ignore quad-core CPUs for the next few years. Dual-core CPUs should net performance gains with modern games (and are more than sufficient to run older games). Quad-core CPUs should net performance losses with almost all existing games, and most games under development.