The gateway between a processor and other parts of the computer is a set of interface controllers generically called the chipset. Traditional chipsets include a Northbridge, with a memory controller and either a PCI Express or an AGP interface for graphics, and a Southbridge, containing the standard PCI controller and various peripheral/communications buses for networking, audio and other components.

Though single-component chipsets have been around for many years, AMD's CPU-integrated Athlon 64 memory controllers removed one task from the Northbridge, making it easier for companies to integrate Northbridge and Southbridge components into one part. The word "set" might not semantically apply to a single-component, but the term "chipset" is still used.

The Northbridge

Traditional Northbridge designs include a memory controller linked directly to the CPU through the Front Side Bus. Early chipsets used a common CPU and memory bus frequency, so that the entire pathway was often called the Front Side Bus. Later chipsets allowed separate CPU and memory bus frequencies, limiting the acronym "FSB" to the pathway between CPU and Northbridge. AMD later removed the memory bus entirely from the chipset in its Athlon 64, with separate Northbridge and RAM pathways on the CPU replacing the Front Side Bus.

What remains common to all Northbridge designs is an AGP or PCI Express controller and a Southbridge interface (internal on single-component chipsets). Some Northbridge designs also incorporate a graphics processor, using either AGP or PCI Express interfaces internally. Integrated AGP graphics is disabled whenever a card is used in the optionally-available AGP slot, but some PCI Express integrated controllers allow simultaneous use of onboard graphics and add-in PCI Express x16 cards for multiple displays.

Single Data Rate Northbridge Technologies (S370)

Socket 370 is still (scarcely) supported and uses a single-data-rate (SDR) Front Side Bus that's perfectly matched to SDR SDRAM, such as 133 MHz Front Side Bus speed and PC133 SDRAM memory. Later chipsets used DDR SDRAM (double data rate), because the newer RAM type offered double the bandwidth. These chipsets support either AGP or PCI graphics, often including onboard AGP graphics.

Double Data Rate Northbridge Technologies (S462)

Socket 462 (Socket A) uses a double-data-rate front side bus that matches quite nicely to DDR SDRAM. AMD often used the data rate, rather than clock rate, to denote the processor's bus speed, with 100, 133, 166 and 200 MHz clock rates listed as 200, 266, 333, and 400 MHz DDR speeds respectively. Single Data Rate SDRAM (PC100/PC133) chipsets existed in early boards, but most are too old to support recent processors and don't play an important role anymore.