Functions of South Bridge

South Bridge is a chipset that is used for controlling I/O Functions such as USB, disk interfaces, PCI Bus, Super I/O Chip support etc. In other words it works as peripheral controller. The main feature of Southbridge is that same South Bridge can be used with different types of North bridges. It is generally located at the lower edge of the motherboard.

Following are some Major Functions Performed by South Bridge:

I/O Control: South Bridge is the key point that decides which kinds of buses, at what speed, and which features will be supported by the system. South bridge controls PCI and ISA buses and transfers information to them or from them.

USB Ports Control: USB Support on the motherboard is provided by the south bridge and which is the main interface for mostly peripheral devices.

Bus Bridge Support: Two main type of buses ISA and PCI are used in most of the modern computers. Since, there is a great speed mismatch between them. South Bridge provides the feature of connecting these two dissimilar buses. This is achieved by PCI-to-ISA bridge chip.

Functions as Interrupt Controller: Interrupt is a CPU request generated by either a Hardware or Software. Interrupt controller is used to decide which request will be serviced first, how will be serviced and how other requests will be handled.  For this purpose generally PIC 8259 is used. South Bridge incorporates all the features of PIC Intel 8259 and reduces manufacturing cost and extra space requirements on the motherboard.

Functions as DMA Controller: DMA is the function of chipset that provides a way to transfer data between I/O device and memory without the involvement f CPU. This functionality is not supported by most of the peripherals and is replaced with a new technique called Bus Mastering. Bus Mastering is a technique in which device not only transmits data to memory directly but actually takes control of buses and performs transfers itself without using DMA controller. This Bus Mastering feature is also Provided by the South Bridge.

ATA/IDE Interface Support: South Bridge provides two IDE interfaces where four HDD can be connected, two HDDs at each interface in Master slave mode. These drives are on PCI bus and save an expansion slot, which also reduces the cost.

Power Management: Another important feature of South Bridge is Power Management to reduce amount of power used by PC during idle periods.

Plug n Play Device Support: This feature allows Automatic detection of new devices to Operating System and BIOS. Detected devices are than assigned appropriate resources such as IRQ,I/O Port Addresses and DMA Channels.

Audio Sound Interface: Interfacing support of Audio device such as High Definition sound devices is also provided by the South Bridge.

Ethernet Support: South Bridge also provides support for interfacing Ethernet ports on the motherboard and its control.