The South Bridge
The south bridge chip, also called ICH (I/O Controller Hub) or PCH (Platform Controller Hub) is connected to the north bridge (or the CPU, in the case of current Intel CPUs) and is in charge of controlling I/O devices and on-board devices, such as:
- Storage ports (Parallel and Serial ATA ports)
- USB ports
- On-board audio (*)
- On-board LAN (**)
- PCI bus (if available)
- PCI Express lanes (if available)
- Real time clock (RTC)
- CMOS memory
- Legacy devices such as interrupt controller and DMA controller
- ISA slots on old motherboards
(*) If the south bridge has a built-in audio controller, it will need an external chip called a codec (short for coder/decoder) to operate. Read our “How On-Board Audio Works” tutorial for more information. Some high-end motherboards use an external audio controller, which is connected to the south bridge chip through a PCI Express x1 lane.
(**) If the south bridge has a built-in network controller, it will need an external chip called a “PHY” (short for “physical”) to operate. Most motherboards use an external network controller connected to the south bridge chip through a PCI Express x1 lane.
Other integrated devices the motherboard may have, such as additional USB, SATA, and network controllers, will be connected to the south bridge chip through individual PCI Express x1 lanes. (On some motherboards these devices may be connected to the north bridge chip instead, if the PCI Express controller embedded in the north bridge chip has plenty of PCI Express lanes.)
The south bridge is also connected to two other chips available on the motherboard: the ROM chip, also known as the BIOS chip (BIOS is one of the programs written inside this chip), and the Super I/O chip, which is in charge of controlling legacy devices such as serial ports, parallel ports, floppy disk drives, and PS/2 ports for keyboard and mouse.
In Figure 6, you can see a diagram explaining the role of the south bridge in the computer.