What is the difference between a dual core i5 and a dual core i7 processor?

I am looking for a good light weight laptop for college next year and i have my eyes set on the Sony VAIO S series (or the ENVY 14 if it ever gets sandybridge). My question is about what kind of performance I could expect from the S series, mainly its new i7 and AMD 6630m graphics.What is the difference between a dual core i5 and a dual core i7 processor?
No such thing as a dual-core i7. Only quad-core i7's. Did you mean i5 quad VS. i7 quad? If you meant that, then cache size and hyperthreading is the primary difference between the two.

EDIT: Ahh ok, makes sense then. I'm honestly not that familiar with the new mobile Sandy Bridge i7's, just the desktop ones. But according to the link, it features hyperthreading (virtual cores). And i5's don't support hyperthreading by default. So I'm going to guess that that's the difference... still.What is the difference between a dual core i5 and a dual core i7 processor?
I7 is faster then i5 Processor

I have a few that I would recommend and they have great price tags:



HP 17-1181NR 17-Inch Envy Notebook PC

*Intel Core i7-720QM Processor, 1.60GHz

*ATI Mobility Radeon HD 5850 Graphics with 1GB Dedicated Video Memory

*750GB (5200RPM) Hard Drive

*6GB DDR3 System Memory

*Genuine Windows 7 Home Premium 64-bit