Datasheet

10 Chapter 1
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Personal Computer System Components
The term bus is also used in any parallel or bit-serial wiring implementation where multi-
ple devices can be attached at the same time in parallel or in series (daisy-chained). Examples
include Universal Serial Bus (USB), Small Computer System Interface (SCSI), and Ethernet.
Chipsets
A chipset is a collection of chips or circuits that perform interface and peripheral functions
for the processor. This collection of chips is usually the circuitry that provides interfaces for
memory, expansion cards, and onboard peripherals and generally dictates how a mother-
board will communicate with the installed peripherals.
Chipsets are usually given a name and model number by the original manufacturer. For
example, if you see that a motherboard has a VIA KT7 chipset, you would know that the
circuitry for controlling peripherals was designed by VIA and was given the designation
KT7. Typically, the manufacturer and model also tell you that your particular chipset has a
certain set of features (for example, onboard video of a certain type/brand, onboard audio
of a particular type, and so on).
Chipsets can be made up of one or several integrated circuit chips. Intel-based moth-
erboards typically use two chips, whereas the SiS chipsets typically use one. To know for
sure, you must check the manufacturer’s documentation.
The functions of chipsets can be divided into two major functional groups, called
Northbridge and Southbridge. Let’s take a brief look at these groups and the functions they
perform.
Northbridge
The Northbridge subset of a motherboard’s chipset is the set of circuitry or chips that per-
forms one very important function: management of high-speed peripheral communications.
The Northbridge subset is responsible primarily for communications with integrated video
using AGP and PCI Express, for instance, and processor-to-memory communications. There-
fore, it can be said that much of the true performance of a PC relies on the specifications of the
Northbridge component and its communications capability with the peripherals it controls.
When we use the term Nor thbridge, we are referring to the set of chips and
circuits that make up a particular subset of a motherboard’s chipset. There
isn’t actually a Northbridge brand of chipset.
The communications between the CPU and memory occur over what is known as the
frontside bus (FSB), which is just a set of signal pathways between the CPU and main
memory. The clock signal that drives the FSB is used to drive communications by certain
other devices, such as AGP and PCI Express slots, making them local-bus technologies. The
backside bus (BSB), if present, is a set of signal pathways between the CPU and Level 2 or
3 cache memory. The BSB uses the same clock signal that drives the FSB. If no backside bus
exists, cache is placed on the frontside bus with the CPU and main memory.
The Northbridge is directly connected to the Southbridge (discussed next) and helps to
manage the communications between the Southbridge and the rest of the computer.
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