The Northbridge and Southbridge chips comprise what is known as a chipset on modern computers. The chipset is responsible for facilitating communication between the computer processing unit (CPU) and the various components on the motherboard, acting as traffic cops and controllers. Since the Northbridge is working constantly, it can become very hot and in many cases it has its own heatsink. Other names for the chip include the Memory Controller Hub (MCH) and the Integrated Memory Controller (IMC).
This chip is located closest to the CPU and controls the fastest components on the motherboard: the CPU, video card slot, and random access memory (RAM). If the CPU cache is found on the motherboard, it also falls under the control of the Northbridge, as does the Southbridge chip. These components are all connected via pathways known as buses, making the bus speed of the computer an important specification in overall performance.
The Southbridge handles the slower traffic on the computer, or the I/O (in and out) devices. SATA and IDE hard drive and expansion slots, RAID, USB, FireWire®, direct access memory (DMA) controller, system clock, power management, interrupt controller, and audio codecs all fall under the control of the this chip. It is also referred to as the I/O Controller Hub (ICH) or Platform Controller Hub (PCH).
While people are used to thinking of the CPU as being the most important element on a motherboard, it’s actually the Northbridge that dictates which type of CPU and RAM can be used on the motherboard. Overclocking ability also depends on the chip. The Southbridge dictates which features the computer will have, and whether or not the newest technologies will be supported. Since only one or two Southbridge chips can be paired with a particular Northbridge chip, the entire system is essentially based around that one chip.
Due to the overriding influence of the chipset, many people choose their computer systems based on the chipset manufacturer that might develop a reputation for excelling in one area or another, usually in graphics support. There is no industry standard for chipset design, driving creative competition between the major manufacturers. Some current designs have incorporated both chips into a single die. Another trend is to include a graphics processing unit (GPU) in the chipset, which saves the CPU from having to process the great amounts of data required for high-definition rendering.