North Bridge Operation
The motherboard north bridge coordinates the interface between the system CPU, system memory, the graphics bus, and the motherboard south bridge. The handling of these tasks compliments the processing power of the CPU and contributes to the operating efficiency of the entire system. Some modern CPUs have eliminated the need for the motherboard south bridge by integrating its functions into the north bridge in the Intel hub architecture, improving the overall efficiency of the system.
Because of the unique way the motherboard interacts with the CPU, memory, and graphics bus, most chips are only compatible with a limited number of CPU models and memory and bus configurations. This usually means that the advent of a new CPU requires the simultaneous development of a new motherboard chipset. Because of this, it is possible for some CPU chips to be delayed in release to motherboard makers while the manufacturer works on completing development and production the north bridge.
Unlike the north bridge, the motherboard south bridge traditionally does not connect directly to the CPU. Because the speed of I/O functions on the motherboard is not as sensitive to the operation of the computer as is the speed of the memory and graphics buses, the south bridge is usually located farther away from the CPU, to the "south" of the PCI bus, leaving the area closer to the CPU for the north bridge and supporting components.
Because of the operating speed of the north bridge, the chip usually generates a lot of heat while in operation, often requiring that a dedicated heat sink and sometimes a fan, be affixed to it to ensure safe operation. The heat sink and its proximity to the CPU make the motherboard north bridge fairly easy to identify.
Image Credit: Wikimedia Commons/Rosco