What is northbridge, southbridge, how northbridge, southbridge works?

The Northbridge is a controller chip used to deal with the interaction among the CPU, RAM, the L2 or Level 2 cache, BIOS ROM, and PCI Express, and the AGP, Accelerated Graphics Port, which are the components that benefit most from fast communication with the processor. It uses the FSB, fast Front Side Bus, to link the various components. Some northbridges also contain integrated video controllers, also known as a GMCH, Graphics and Memory Controller Hub, in Intel systems. Because different processors and RAM require different signalling, a northbridge will mainly work with only one or two classes of CPUs and only one type of RAM in general.

The northbridge is important for how far a computer can be overclocked, as its frequency is used as a baseline for the CPU to establish its own operating frequency. This chip's temperature will increase as processor speed becomes faster and cooling measures need to be implemented. CPUs cannot be overclocked infinitely, as digital circuits are limited by physical factors such as propagation delay which increases with operating temperature, therefore most overclocking applications have software limitations which limit the multiplier and external clock setting.

The southbridge, also called ICH, I/O controller hub, in Intel systems, AMD, VIA, SiS and other motherboard, is a chip used to implement the "slower" capabilities of the motherboard in a northbridge/southbridge chipset computer architecture. The southbridge is not directly connected to the CPU, which is different from that of the northbridge and the northbridge ties the southbridge to the CPU. Through the use of controller integrated channel circuitry, the northbridge can directly link signals from the I/O units to the CPU for data control and access.

With the southbridge being removed from the CPU, it is often used for the slower devices on a typical microcomputer. A particular southbridge will often work with several different northbridges, but these two chips must work together. There is no industry-wide standard for interoperability between different core logic chipset designs. Traditionally this interface between northbridge and southbridge was simply the PCI bus, but since this created a performance bottleneck, most current chipsets use a different interface with higher performance.

The Southbridge handles more basic, slower, forms of I/O, such as serial ports, USB ports, and IDE. The Southbridge is attached to the Northbridge's PCI bus.

The Northbridge-Southbridge chips greatly increase the speed of modern computers. You will find them on almost all current computers like Intel chipsets, VIA, and AMD chipsets. In a word, the Northbridge-Southbridge together forms a basic minimum architecture for a modern computer.

The computers using Intel's new IHA, Intel Hub Architecture are exceptions. IHA, like Northbridge-Southbridge, uses two chips which are called hub controllers to deal with communications between the processor and the other system components. However, the GMCH, Graphics and AGP Memory Hub, the equivalent of the Northbridge, doesn't handle the PCI bus. That is now handled by the ICH, I/O Controller Hub, which sits on a bus and is two times faster than the Southbridge's bus. Another important factor is that the IHA bus can detect different data types as they move over the bus and optimize its bus performance.