[sspiff]

They stopped licensing the interfaces used to connect to the different parts together (north bridge <-> south bridge and north bridge <-> CPU) starting with Nehalem (first generation of Core i[N] processors).

This effectively meant that if you wanted to build a mainboard for Intel CPU's, you had to buy the chipsets from Intel as well.

Before that, you could buy mainboards with ATI (Xpress), nVidia (nForce), or VIA chipsets. All of these could integrate different SATA contollers, audio chips, USB busses, etc.

By not licensing their interfaces, Intel basically took over almost all of that market by locking others out of it. I believe they could only do this because they had no real competition from AMD anymore in the CPU market.