NORTHBRIDGE AND SOUTHBRIDGE
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The northbridge is usually paired with a southbridge, also known as I/O controller hub. In systems where they are included, these two chips manage communications between the CPU and other parts of the motherboard, and constitute the core logic chipset of the PC motherboard.
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Northbridge
The northbridge alternatively referred to as the PAC (PCI/AGP Controller) and nb, the northbridge is an integrated circuit responsible for communications between the CPU interface, AGP, and the memory. Unlike the Southbridge the Northbridge is directly connected to these components and acts like a "bridge" for the Southbridge chip to communicate with the CPU, RAM, and graphics controller. Today, the northbridge is a single-chip that is North of the PCI bus, however, early computers may have had up to three separate chips that made up the northbridge.
The northbridge and southbridge commonly have a heat sink; 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 need to wait to read the memory over the front side bus (FSB).
Southbridge
The southbridge is an IC on the motherboard responsible for the hard drive controller, I/O controller and integrated hardware. Integrated hardware can include the sound card and video card if on the motherboard, USB, PCI, ISA, IDE, BIOS, and Ethernet. The southbridge gets its name for commonly being South of the PCI bus.
Difference between northbridge and southbridge
Northbridge is directly connected to the CPU, and it allows the CPU to interface with the RAM, AGP or PCI Express, and the southbridge. Sometimes Northbridges have integrated video as well. A Northbridge will typically work with only one or two classes of CPUs and generally only one type of RAM.
The southbridge is connected to the CPU through the Northbridge. It implements the "slower" capabilities of the motherboard in a northbridge/southbridge chipset computer architecture, such as the PCI bus, HDD controller, and USB.
Together, Northbridge and Southbridge are your motherboard's chipset. Since they are part of the motherboard, not the CPU, it will only affect your CPU decision insofar as it's important to get a CPU compatible with your motherboard's chipset.
Note: Some newer chipsets are combining the Southbridge and Super I/O chips into a single chip and referring to this chip as the Super Southbridge chip. Some manufacturers such as NVIDIA and SiS have even combined the Northbridge, Southbridge, and Super I/O into a single chip.
Note: New motherboards are replacing the northbridge and the southbridge with IHA.
Note: When choosing a motherboard, you might look at the chipset. Some chipsets are higher performance than others, but the main difference will be in the processor.
