The main difference is the size of the transistors. Sandy bridge (or second gen) had a 32 nm transistor size. Ivy bridge (or third gen) has 22 nm. The main differences is the chipset they use, their GPUs, and their power consumption. SB uses z68, IB uses z77. SB uses Intel graphics 3000, and IB uses 4000, the main difference being the amount of transistors. IB consumes far less power than SB. About 20v less, but it does produce more heat.