The 1st gen Core-i processors are 15-20% faster than their Core 2 counterparts, almost double the multi-threaded performance (thanks to , or the ability of one processor core to handle 2 threads simultaneously as long as the threads don't conflict on resources). Nehalem also moved the memory controller from the chipset onto the processor (improving memory bandwidth) - and moving PCI and DMI controllers onto the chip for mid-range models (completely eliminating the need for the north bridge on the motherboard), replaced the old front-side bus with a faster interconnect path, and improved virtualization capabilities.
2nd gen are based on the microarchitecture. This included graphics being integrated onto the die and added an extra level of cache (as well as increasing the size of the lower level cache), allowed multiple simultaneous memory read/store operations per instruction cycle, introduced which increased parallelism in floating point handling. It has about 10% faster performance compared to Nehalem, but with a lot better graphics and better power management.
3rd gen are based on the , which is primarily just a die shrink of Sandy Bridge, but with again vastly improved graphics capabilities, and targeted toward mobile applications with a nearly 50% reduction in average power consumption for the same level of performance.
In June 2013, Intel is slated to release 4th generation Core processors, codename . Reports already show they have double the graphics performance versus their Ivy Bridge counterparts, and Intel claims their graphics performance is similar to the Nvidia GT650M. Intel also claims that for mobile applications the generation-to-generation battery life increase is greater than any other generation-to-generation battery life increase, claiming upward of 10 hours battery life for ultrabooks. Part of why they the new processors will have better battery life is due to moving the voltage regulator onto the chip instead of leaving it as a function for the motherboard. In addition, Haswell features a new cache design (a hybrid cache-interposer for high graphics bandwidth, cache design codenamed Crystalwell), a new instruction set including and a new set of advanced vectorized extensions.