Typically, the southbridge implements the slower capabilities of the motherboard in a northbridge/southbridge chipset laptop architecture. The problem arises when there have been important modifications in hardware, like altering RAM, CPU and Mobo, then Windows will probably not activate automatically, however you proceed to can. If you purchase a computer with preinstalled key in BIOS and change the mobo with the same one, than you are OK, as far as I know… Even with OEM licenses that aren’t in BIOS, you’ll find a way to change the mobo on failure, but I assume that you can’t improve CPU on the similar time, as it might constitute as “totally different machine”. Hard drives, CD gamers, DVD gamers, PCI bus, and I/O ports are all connected to the Southbridge. The Southbridge regulates what bus and how much data may be passed to the Northbridge.