so i have a core i7 920....its obv. a quad core, but i was talking to some tech guy, and he was talking about i7's have 8 or 12 cores, and i was wondering what exactly that means...my i7 has hyper threading....what does that do....and finally, when i go into dx diag, it says
It's a quad core - there are 4 physical cores. But with Hyper Threading each core can handle 2 threads so it operates like it has 8 cores (although because they are not separate physical cores you cannot say that the performace improves linearly). There are 4 physical cores, but 8 logical 'cores'.
The idea is that once the pipeline is loaded, you can clock it really fast. The problem is that when something called "branch prediction" http://en.wikipedia.org/wiki/Branch_predictor
fails (basically when the CPU guesses wrong about which way the program is going to go), you need to flush the pipeline and start over.
tu, the big improvement came with the Conroe Core2's. A Conroe E6600 running at 2.4 GHz is about 1.5 times faster than a 3.46 GHz P4 per core.