Beginning with the Pentium class 430TX PCIset, Intel divided their future chipsets into two major components: Northbridge and Southbridge. Essentially, the Nothbridge interface with the processor, memory subsystem, cache, AGP, and PCI slots. The task of controlling the I/O and legacy ISA slots is left to the Southbridge. This enables Intel to replace the Southbridge with new controllers (such as the upcoming PIIX6 with Firewire support) without redesigning the entire chipset. And it will allow motherboard designers to choose which Southbridge they wish to use for cost purposes.