An i3 is basically a pentium with hyperthreading. Then you move up to i5 which is a quad core, and an i7 is basically i5 with hyperthreading.
But what about in laptops.. all the i5s I've seen (except in 15" MacBook Pros) are 2 cores, 4 threads. What's the difference between it and an i3, then? Is it just so people who haven't done their research just see the name of the processor and assume it's better?
Also in laptops i7s are 2 cores w/ 4 threads aswell.. what's the difference between all of these?