The first difference is the processor architecture, well some are saying Core i5 and Core i3 are just Core 2 duo with hyper threading and Core i7 is quad core with hyper threading .. yes if you check the out side details that is correct but when you go to the inside it is not true. Lets see the things in detail. In older Mother Boards they used a bridge controllers and it was replaced by the hub architecture.
Core 2 duo and older cpus have communicate the a dev
ice called MCH, Memory Controller Hub which communicates with the CPU, RAM, VGA card and ICH, Input Controller Hub which does the communication with the Hard Disks, Network Cards, Sound Card/s, even the your favorite USB devices.
But with the Core i series processors MCH is biult into the die itself and it has only a ICH, which is called PCH Platform Controller Hub,
Since the cpu can deal with VGA cards and the memory directly, it will be much faster..
