Is the Front Side Bus part of the CPU or the Motherboard?

Something I'm working on wants a very fast/wide Front Side Bus (FSB). What component is the FSB part of? Is it part of the CPU or the motherboard? Is it something that can be placed on a board, or is it fundamentally a part of the motherboard and therefore not able to be replaced?


The Front Side Bus was once the link between the CPU core(s) and the memory controller back when the memory controller was in the Nortbridge. Modern CPUs and motherboards don't have front side buses because the memory controller is now built into the CPU.