Question: what is the difference between core i3 2nd generation and 3rd generation?
Answer: Gen 2 (Sandy Bridge) is based on the older 32 nm process, while Gen 3 (Ivy Bridge) is based on the 22nm process. Basically, the wires got smaller so they could fit a bit more circuitry in there. Comparing similar processors, you get a better integrated graphics chipset in the newer processors (4000 or 2500 vs.