The Northbridge is the controller that interconnects the CPU to memory via the frontside bus (FSB). It also connects peripherals via high-speed channels such as AGP and PCI Express. The Northbridge may include a display controller, obviating the need for a separate display adapter.
The Southbridge controller handles the remaining I/O, including the PCI bus, parallel and serial ATA drives (IDE), USB, FireWire, serial and parallel ports and audio ports. Earlier chipsets supported the ISA bus in the Southbridge. Starting with Intel's 8xx chipsets, Northbridge and Southbridge were changed to Memory Controller and I/O Controller
Northbridge Connects CPU to:
RAM
AGP bus
PCI Express bus
Built-in display Adapter
Southbridge Connects CPU to:
ATA (IDE) Drives
USB bus
FireWire bus
Serial port
Parallel port
Built-in audio
ISA bus (earlier PCs)