The i815 chipset is the fourth Intel chipset to make use of their Intel Hub Architecture (formerly known as Accelerated Hub Architecture - AHA). The first chipset to use Intel’s Hub Architecture was the low-cost i810, followed by the i810E and then the 820/840 solutions as well as the recently released i820E. For those of you unfamiliar with Intel’s Hub Architecture, here is an excerpt from our original i810 review:
The key to the success of the Accelerated Hub Architecture is the substitution of individual hub interfaces for the PCI bus in connecting the various parts of your system to your memory/CPU on the motherboard end of things. Take a look at the acronym PCI, Peripheral Component Interconnect, it doesn't really scream "all-purpose-bus" now does it? Intel took what was once a two-chip solution (North/South Bridge) and converted it into a two chip, three-hub solution, the first implementation being the i810 chipset.
The three individual hubs are the Graphics and Memory Controller Hub (GMCH), the I/O Controller Hub (ICH) and the Firmware Hub (FWH). The two main hubs, the GMCH and the ICH are connected via an internal bus that offers double the bandwidth of the PCI bus, 266MB/s. This is a definite improvement over the "old" way of doing things and will shortly become the new standard as far as chipsets go, don't expect Intel to return to the classical way of doing things on the motherboard level anytime soon.
That description of the AHA is pretty much universal and applies in almost every way to the i815. The i815 differs from the i810’s Hub Architecture in that it uses a different Graphics & Memory Controller Hub (GMCH) (82815 vs. 82810), but it still supports the same ICH and FWH as the i810E and 820E.