Motherboards of all price ranges offer a network interface that is already integrated on the board. The reason? A PCI-based network card is more expensive and takes up a PCI slot. At first blush, the integrated option, in theory, offers nothing but advantages, as very little additional engineering effort is required, the additional costs are minimal and the added value is something users surely don't want to do without. However, the end results of integrated network interfaces, especially for Gigabit Ethernet, are not always so black and white.
Different Network Integration Approaches
The simplest strategy for adding a network controller to the motherboard is by directly integrating the PCI network chip. Integrating the entire logic into a chip set component via the PCI bus, which is part of Southbridge, mostly does this. Mass production usually makes up for the development costs, while the implementation of the interface requires just a small component that allows for the correct physical connection (PHY).
Meanwhile, Intel has created a faster interface and has integrated the logic into the Northbridge for its 865 and 875 chipsets. By doing this, Intel's design does not tax the bus' pipeline between the Northbridge and Southbridge with excessive network data packets.