Before we get into details, we need to explain the groundwork of Intel's architecture. We will start with an explanation of Intel's older architecture, like what the 440BX uses, as this will make the advantages of Intel's new architecture more clear.
The old way of doing chipsets has two components, the northbridge and the southbridge. The northbridge communicates with the CPU over the Front Side Bus (FSB) and acts as the controller for memory, AGP and PCI. The type of FSB, memory and AGP varies from northbridge to northbridge. Some northbridges integrate video as well.
The southbridge takes care of most basic forms of I/O, such as USB, serial ports, audio, IDE and more. What I/O is controlled depends on the specific southbridge. The southbridge sits on the northbridge's PCI bus, which is usually a 32-bit, 33MHz bus capable of providing 133MBps of bandwidth. Intel's 440BX chipset and all current VIA and AMD PC chipsets use this type of northbridge/southbridge architecture.
Instead of the normal northbridge/southbridge setup, for all 8xx series chipsets including the i815 and i815E, Intel designed the Intel Hub Architecture (IHA). Like the old system, IHA has two parts, but they are called the Graphics and AGP Memory Controller Hub (GMCH) and the I/O Controller Hub (ICH) instead of northbridge and southbridge.
The GMCH, like the northbridge, communicates with the CPU over the FSB and acts as a controller for memory and AGP. And also like a northbridge, the GMCH sometimes comes with integrated video. Unlike a northbridge, the GMCH does not come with a PCI controller.
The ICH, like the southbridge, takes care of most basic forms of I/O, such as USB, serial ports, audio, and more. The ICH also takes care of being the PCI controller. The ICH communicates with the GMCH over a 233MBps bus, which is twice the bandwidth of the normal northbridge/southbridge connection. Even more importantly, this new bus can detect different kinds of data, such as streamed audio or hard drive accesses, and optimize the flow of data for those types of audio.