Basically the difference between the 2nd gen (Sandy Bridge) & 3rd gen (Ivy Bridge) is the the following:
1. Slightly lower power consumption.
2. 6% average increase in performance (assuming same clock speed).
3. Improved integrated graphics. Ivy Bridge has either the HD 4000 or HD 2500 depending on the CPU model. Sandy Bridge has either the HD 3000 or HD 2000 depending on the CPU model.
4. Core i5 and Core i7 Ivy Bridge CPUs includes circuitry which supports PCI-e 3.0 slots. The Core i3 Ivy Bridge CPUs only supports PCI-e 2.0 slots. This means if an Ivy Bridge Core i3 CPU is placed in a motherboard with a PCI-e 3.0 slot, it will act as a PCI-e 2.0 slot.
nanometre. The smaller the NM the more transistors that can be fit in and low idle power consumption and you can add more performance by increasing clock speed and architecture on it to get faster performance for less power consumption. 3rd gen is bes, 2nd gen is not bad but 1st gen is ancient power hungry and slow.
That is inaccurate, the 1st gen isn't ancient, the 1st gen i series came out in 2010.
NM stands for Nanometers, this unit is used to measure the CPU die as it is very small.
1 nanometer is a billionth of a meter.
Smaller dies can accept the same amount and more transistors than bigger dies and they can reduce power consumption, heat output (depending on architecture), production cost (more CPU dies are made from a single silicon wafer).