LGA 1366 is Intel's first new desktop socket in four years. It uses the same ZIF design as the familiar LGA 775 architecture, but it incorporates many more contacts.
One reason for this expansion is that with Core i7 the CPU takes over memory controller functions that were previously handled by the north bridge. In place of the old front side bus it now has a dedicated high-speed connection directly to the system RAM, just like the HyperTransport used by AMD processors. Intel calls its new bus the QuickPath Interconnect (QPI).
It's worth noting that Core i7 is Intel's first DDR3-only platform. It uses a three-channel memory controller, so you can expect to see DDR3 DIMMs appearing in three-packs soon. You don't have to install modules in threes, but if you do you can expect a small performance benefit, as with existing dual-channel controllers.
These big architectural changes are backed up by some less visible advances. Until now, Intel's quad-core processors have been constructed from two dual-core dies, but now Core i7 brings together four cores on a single die. It's also Intel's first processor design to use an L3 cache, shared between all four cores.
The icing on the i7 cake is a pair of logic features found on neither the Phenom nor the Core 2. The first is Intel's HyperThreading (HT) technology, and the second is a new feature called Dynamic Speed Technology, which allows the processor to detect when load is unevenly balanced and automatically boost the speed of the cores with the most work to do. Idle cores are clocked down to keep power consumption within tolerance.