PC - Motherboard (II)

Choosing The Right Chipset


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.

Example of an intel chipset. 440BX Chipset was very popular in motherboards for iPentium II

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 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.

Nvidia chipsets normally offer higher performance than chipsets of SiS or Via

Intel Quad Data Rate Northbridge Technology

Intel's quad-pumped quad data rate bus transfers data four times per clock cycle, so that 100, 133, 200 and 266 MHz clock rates provide effective 400, 533, 800 and 1066 MHz data rates. Because CPU Front Side Bus data rates are often twice as high as those of DRAM data rates, the performance solution has been to double the memory bus width from 64 to 128 bits by placing two modules on parallel pathways, which involves a technology called dual channel mode.

As an example, two DDR400 (PC3200) memory modules in dual-channel mode have the same bandwidth as Intel's FSB800 CPU bus, and both operate at an actual clock rate of 200 MHz. The same can be said of matching two DDR2-533 modules in dual-channel mode to Intel's FSB1066 Front Side Bus.

We recommend choosing a dual-channel supporting chipset if you want to opt for such a solution. Current PCI Express Northbridge technology supports DDR2-SDRAM in dual-channel mode.

This is a scheme of a Via chipset for AMD Athlon 64 where we can see most of the features supported by current motherboards

HyperTransport Interconnect Technologies (S754, S939, AM2)


With the memory bus removed from the Northbridge, AMD chipsets are able to mix-and-match older and newer technologies far more easily. AGP chipsets originally destined for use with Socket 754 have also been made available for Socket 939 buyers, PCI Express chipsets designed for Socket 939 have been used in Socket 754 motherboards, and AM2 motherboards using the previous Socket 939 generation of chipsets are available.


The Southbridge


The Southbridge contains most peripheral, multimedia, and communications busses, including the PCI controller (Peripheral Components Interconnect), ATA controller (for hard drives and optical drives), USB controller (Universal Serial Bus for external devices), network controller interface, audio controller interface, and often even a modem interface. Most chipsets from any given time period offer similar performance, but reviews can inform the buyer of potential inadequacies, such as which recent Southbridge designs had the worst Serial ATA performance, and which had sub-par USB performance.

Another feature of current motherboards is RAID mode for Serial ATA controllers, which allows the user to run up to four drives in a secure or high-performance array.

Gigabit networking is now mature, and most chipsets include dedicated links to a Gigabit PHY (physical chip, which takes care of the physical connection). High-end chipsets typically feature two links for two gigabit connections