NORTHBRIDGE & SOUTHBRIDGE

Northbridge

Sometimes abbreviated as nb, the northbridge is an integrated circuit (e.g., Intel or VIA) that is responsible for communications between the CPU interface, AGP, PCI, and the memory. The northbridge gets its name for commonly being North of the PCI bus. Below is a graphic illustration of the ASUS P5AD2-E motherboard and some basic explanations of each of the major portions of the motherboard, including the northbridge. As shown in the picture below, it's common for the northbridge and southbridge to have a heatsink; in addition, the northbridge is usually slightly larger than the southbridge and is the closest to the CPU and memory.

When the CPU needs data from RAM, a request is sent to the northbridge memory controller. After the request has been received, it responds with how long the processor will need to wait in order to read the memory over the front side bus (FSB). Some newer motherboards have replaced the northbridge and the southbridge with IHA.

Southbridge

An integrated circuit (e.g., Intel or VIA) on the motherboard that is responsible for the hard drive controller, I/O controller and integrated hardware such as sound card, video card if present on the motherboard, USB, and Ethernet. The Southbridge gets its name for commonly being South of the PCI bus. Below is a graphic illustration of the ASUS P5AD2-E motherboard and some basic explanations of each of the major portions of the motherboard including the southbridge. As shown in the below picture, it's common for the northbridge and southbridge to have a heatsink; in addition, the northbridge is usually slightly larger than the southbridge.

Although the southbridge handles a lot of the I/O devices, slower and less prominent input/output devices, such as the serial port, keyboard, and non-USB mouse are handled by the super input/output (SIO).
Some newer motherboards have replaced the northbridge and the southbridge with IHA.