Page 65 - A Practical Guide from Design Planning to Manufacturing

Computer Components 41

Chipsets

The chipset provides a vital layer of abstraction for the processor. Instead
of the processor having to keep up with the latest hard drive standards,
graphics cards, or DRAM, it can be designed to interface only with the
chipset. The chipset then has the responsibility of understanding all
the different bus standards to be used by all the computer components.
The chipset acts as a bridge between the different bus standards; modern
chipsets typically contain two chips called the Northbridge and
Southbridge.
The Northbridge communicates with the processor and the compo-
nents requiring the highest bandwidth connections. Because this often
includes main memory, the Northbridge is sometimes called the Memory
Controller Hub (MCH). The connections of a Northbridge typically used
® ®
with the Pentium 4 or Athlon XP are shown in Fig. 2-1.
In this configuration, the processor communicates only with the
Northbridge and possibly another processor in a multiprocessor system.
This makes bus logic on the processor as simple as possible and allows
the most flexibility in what components are used with the processor. A
single processor design can be sold for use with multiple different types
of memory as long as chipsets are available to support each type.
Sometimes the Northbridge includes a built-in graphics controller as
well as providing a bus to an optional graphics card. This type of
Northbridge is called a Graphics Memory Controller Hub (GMCH).
Including a graphics controller in the Northbridge reduces costs by
avoiding the need to install a separate card, but it reduces performance

Processor
(optional) Processor
Processor
bus
Chipset
Graphics Memory DRAM
Graphics bus Northbridge bus main
card memory

Hub
bus

Southbridge

Figure 2-1 Northbridge (MCH).