Below is a response I made to a member who asked what is the difference is between an AMD Phenom II x4 and a Core i7 Socket 1366. To begin to understand that difference, you must understand Bus Speeds. Please note: this does not cover everything, and it is solely intended to give the Novice Builder an explanation of how to determine System Speed, Bottlenecks, and what components to choose when upgrading or building from scratch. Enjoy!
The answer doesn't always lie in the clock rate of a processor, i.e. 2.8ghz. The single most important part and the "BASE" of any good computer lies in it's FSB, QPI, or HT's. Did I lose you yet?
FSB = Front Side Bus (Intel just moved away from this)
QPI = Quick Path Interconnect (Intels new baby introduced by the Nehalem processors I believe)
HT's = Hyper Transports (AMD's version of FSB or QPI, or vice versa)
The difference between the three is very technical and you just about need an engineering degree to understand it. So I don't have to get in the argument of what makes FSB, QPI, or HT's different, I'll compare two processors with different FSB's to help you understand the question, "what is the difference is between an AMD Phenom II x4 and a Core i7 Socket 1366". To begin to even comprehend that difference, you must fully understand this...
Motherboards System Bus (FSB) is 800mhz.
It comes with a 2.8ghz processor with a FSB of 533mhz
The RAM is DDR PC 2700 which is 333mhz. 1GB (2 x 512mb)
Starting to see where the term bottleneck comes from? Ideally you want all of these components mhz speeds to be as high as allowed by its maximum, which is the motherboards System Bus, specific CPU's Supported, and Memory speeds supported (it is often the memory controller on the motherboard that limits the memories speeds).
System 2 (I'm going to upgrade System 1)
I leave the motherboard alone, System Bus is 800mhz
I upgrade to a 2.6ghz processor with a FSB of 800mhz that is supported by the motherboards chipset according to the motherboards manufactures website.
I find out on the same website that the boards memory controller allows for PC 3200 DDR which is 400mhz and that the board has two memory slots that support a maximum of 2GB per slot. So I buy 4GB (2 x 2gb) of PC 3200 DDR.
Now my system is quite speedy. Even though the clock rate on the processor is actually .2ghz slower, my FSB has increased considerably, so I'm cooking pretty good now. Also, I have more GB's of RAM to allow for better multi-tasking (multiple programs open at the same time) and any program using that memory will run at 67mhz faster than System 1's did.
So as you can see, it's not always about the processor.
What is the difference between a 2.8GHz quadcore i7 and a 2.8GHz quadcore Phenom II? Is the difference that big? Is it worth the money?
Core i7 Socket 1366 processors run at a QPI of 4.8GT/s usually on X58 chipset boards that support a QPI of 6.4GT/s. Phenom II x4 run at 4000mhz HyperTransports on motherboards usually supporting 2600mhz Transports.
The level of cache and size of that cache also matters. L3 is better than L2. So always compare that when shopping.
To date, it is pretty well known that the Core i7 Socket 1366 line up of processors are the fastest in the world. But overkill for many people. It's cheapest processor is about $300.
Phenom II x4 are up there on the list, AMD's fastest processor. You can find a speedy one for much less than $300. So on the Intel side, the Core i7 920 for only $300 is an awesome "bang for your buck", but many people/gamers will often go the cheaper route of AMD which will provide plenty of bang, for even less dollars.
If you are an extreme enthusiast and want the best of the best, then go Intel Core i7 Socket 1366. If you want a nice system with high FPS but won't necessarily provide as big of a WOW factor, go AMD Phenom II x4.
Finally, have a look at TomsHardware.com CPU HIERARCHY CHART March 2010 so you can see where ALL of the processors are ranked in speed to one another. Hope that helps some, and sorry if the explanation was long or too technical.