bridge - How is the communication between northbridge and southbridge like?

How is the connection/communication between northbridge and southbridge like?

1. It seems that data must pass from the CPU to the northbridge, and then again over a PCI bus to the southbridge, based on a picture from http://en.kioskea.net/contents/pc/bus.php3

   

2. It seems that data pass from the CPU to the northbridge, and then again over a internal bus to the southbridge, based on a picture from http://en.wikipedia.org/wiki/Motherboard#Integrated_peripherals

   

So the two seem to agree with each other. I wonder which one is correct?

Thanks!

Both answers are correct, although answer 2 is the modern implementation.

Answer 1 shows why do we call the components northbridge and southbridge: One used to lay on one side of PCI bus, and another used to lay on another side of the bus, while the bus was an essential part of the computer, similarly to equator on earth. Recently, however, Intel and AMD optimized this connection and so there is a proprietary connection between the northbridge and the southbridge. It's marked as internal connection on the second diagram.

Intel's internal connection is called Direct Media Interface, and connects memory controller hub (MCH, in the northbridge, and recently in CPUs) with the I/O controller hub (ICH9, in the southbridge) proved in 1.3.3 Direct Media Interface

AMD employs solution called Unified Media Interface, as shown on the diagram on page 4 of the product brief

So yes, data passes through front side bus, either QPI for Intel or HT for AMD, and then through the internal bus to the southbridge

Both diagrams display a possible motherboard layout. For any given model, one of them might be correct. Many modern motherboards don't even have a Northbridge...

From Chipset Basics: Meaning And Functions - Tom's Hardware:

For years, the PCI bus was used as the connection to the Southbridge. However, its bandwidth is no longer sufficient for today's requirements, so the chip makers all offer their own solutions (e.g., VIA's V-Link, SiS's MuLTIOL, Intel's i-Link and AMD/NVIDIA's HyperTransport).

Currently, the Southbridge contains at least a PCI controller, floppy/ IDE/ hard disk controllers, serial and parallel ports, USB support and power management functions. [...]

(emphasis mine)