Hardware Reference
In-Depth Information
The North Bridge is sometimes referred to as the PAC (PCI/AGP Controller). It is essen-
tially the main component of the motherboard and is the only motherboard circuit besides
the processor that normally runs at full motherboard (processor bus) speed. Most modern
chipsets use a single-chip North Bridge; however, some of the older ones actually consis-
ted of up to three individual chips to make up the complete North Bridge circuit.
The South Bridge is the lower-speed component in the chipset and has always been a
single chip. The South Bridge is a somewhat interchangeable component in that different
chipsets(NorthBridgechips)oftenaredesignedtousethesameSouthBridgecomponent.
Thismodulardesignofthechipsetallowsforlowercostandgreaterflexibilityformother-
boardmanufacturers.Similarly,manyvendorsproduceseveralversionsofpin-compatible
South Bridge chips with different features to enable more flexible and lower-cost manu-
facturing and design.
The South Bridge connects to the 33MHz PCI bus and contains the interface or bridge to
the 8MHz ISA bus (if present). It also typically contains dual ATA/IDE hard disk control-
lerinterfaces, oneormoreUSBinterfaces, andinlater designseventheCMOSRAMand
real-timeclockfunctions.Inolderdesigns,theSouthBridgecontainedallthecomponents
that make up the ISA bus, including the interrupt and DMA controllers.
