What users wanted was a true 440BX successor. They wanted a chipset that had the best of both the i810 and i820 worlds; more specifically, support for the 133MHz FSB, PC133 SDRAM support and AGP 4X support. This time, Intel heard these cries and went to work developing what will eventually be called the i815 chipset. Like its name suggests, it is a chipset that borrows features from both the i810 and i820 chipsets, plus a little extra on the side.

The i815 also utilizes Intel's new Hub Architecture, much like its i810 and i820 siblings do. Unlike the older 2-chip "North Bridge" and "South Bridge" combination that was used with Intel's older chipsets and still is being used by VIA and other chipset makers, the Intel Hub Architecture is a 2-chip, 3-controller (or "hub) architecture. These 3 hubs include the Graphics and Memory Controller Hub (GMCH), the I/O Controller Hub (ICH) and the Firmware Hub (FWH).

So, what does this all mean and what type of an advantage does the new Hub Architecture have over the traditional North Bridge and South Bridge chipsets? Let me explain.

Intel Hub Architecture Explained
Let me first run through the architecture of the North Bridge/South Bridge so you have some room to make comparisons. The North Bridge is what controls the CPU, system memory, AGP bus and anything else that talks directly with the system memory and CPU-it also includes support for the PCI bus. This PCI bus includes all the PCI expansion slots on the board, the ISA bus and its expansion slots and the Southbridge controller that controls your I/O devices such as IDE, USB and Firewire devices. All of these devices go through the PCI bus, which is only capable of 133MB/s total throughput (skipping the math that's involved to calculate this) and into the North Bridge chip for interface with the CPU, AGP or system memory. As you can see, this 133MB/s bandwidth becomes a bottleneck when taking into consideration of how many different buses and devices are plugged into and using the PCI bus.

North Bridge/Sound Bridge Architecture

The answer to this aging problem? Intel's Hub Architecture! With the Hub Architecture, Intel has reorganized the different buses and controllers for more efficiency.

First off, we have the Graphics and Memory Controller Hub, which is essentially the equivalent of the North Bridge. It controls the CPU, system memory, AGP bus and anything else that interfaces directly with the CPU and system memory. So far, everything seems pretty much the same-but that's soon to change.

Along comes the I/O Controller Hub, which can be considered as the equivalent of the South Bridge. The difference, however, is that it does not interface with the Graphics and Memory Controller Hub through the slow, 133MB/s PCI bus, but through its own dedicated channel that's capable of double that throughput, 266MB/s. As we move down, the PCI bus is now connected to the I/O Controller Hub, along with the usual I/O buses and controllers such as IDE, USB and Firewire. All of these buses and controllers interface through the I/O Controller and communicate with the Graphics and Memory Controller Hub through the dedicated 266MB/s channel. One interesting fact to note is that with the Hub Architecture, Intel has completely removed native support for ISA slots, which, in my mind, is a good move. Manufacturers, however, can add support for ISA slots on their motherboards by using an ISA to PCI bridge controller, but most manufactures have chosen the same route as Intel of abandoning the ISA bus.

The last piece of the puzzle is the Firmware Hub. This little chip, which is capable of storing 4Mb of data, is basically a CMOS chip for storing the BIOS and communicates through the I/O Controller Hub.

Intel Hub Architecture

i815 and i815E - Specific Features
There are 2 versions of the i815 chipset, the i815 and the i815E. Both of these are identical in their use of the Graphics and Memory Controller Hub and the Firmware hub, but the difference lies in the I/O Controller Hub that each utilizes. The i815 uses the original ICH, which is also used in the i810 and i820 chipsets, has support for ATA-66 and has a USB controller for support of up to 2 USB ports while the i815E uses the new ICH2, which is also used in the newer i820E chipset and has support for ATA-100 and 2 USB controllers with support for up to 4 USB ports.

The ASUS CUSL2 board that we have here uses the newer i815E chipset.

Both chipsets have support for up to 512MB of memory, which shows that Intel was not aiming this product in the high-end market--but 512MB of memory should be enough for almost everyone. They also include built-in AGP video in the form of a modified version of a 2-year-old Intel graphics controller. The integrated video is a very-poor performing, 1MB VRAM (shared with main system memory) solution for OEM's, so most of you would probably want to plug in a nice high-performing AGP card of some sort in there. Once an AGP card is plugged in, the on-board video will disable itself.

One of the most significant features of the i815/i815E chipsets is that they support asynchronous operation of the system memory and the front side bus. With this neat feature, the user can run the memory either 33MHz higher than the 66MHz FSB when using a Celeron or 33MHz lower than the 133MHz FSB when using Coppermine Pentium III's. This can be useful for those people who have PC100 memory and would like to either gain some performance when running it with a Celeron or save some money by not having to go out and buy PC133 memory to go with their new Coppermine Pentium III's (of course, when running a 133MHz FSB Coppermine Pentium III with PC100 SDRAM, you'll be losing some performance when compared to using PC133 SDRAM). Unfortunately, for you people who have PC66 SDRAM and would still like to use it with their Celeron processors, you're going to be at a loss because Intel has removed support for PC66 memory in these chipsets. If you wish to upgrade to an i815/i815E motherboard such as the CUSL2 we're reviewing here, you're going to have to throw away that PC66 SDRAM and buy either PC100 or PC133 SDRAM.

On to: Introducing the ASUS CUSL2