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NVIDIA's nForce4 SLI Intel Edition chipset

The green team dips its toe in the big pond

CORE LOGIC CHIPSETS. I've spent the last six days knee deep in 'em, those unappreciated chips that glue everything together inside of a system. Back in my Amiga days, the core logic chips were stars, a constellation of sexy custom chips that provided what was then considered amazing audio and fluid, colorful graphics. But that was long ago. Nowadays, core logic chips aren't considered very exciting, except by what they enable the more exciting chips, like CPUs and GPUs, to do. Fortunately, the nForce4 SLI Intel Edition's would-be role as an enabler is quite the proposition: this chipset will allow a Pentium 4 processor to team up with a pair of GeForce 6 GPUs in SLI mode and pump out tasty eye candy by the bucketload.

That capability is currently unique in the Pentium 4 chipset world, in part because NVIDIA holds the reins of the SLI bandwagon, and—for perfectly valid technical reasons, mind you—the company hasn't allowed its multi-GPU mode to operate on competing chipsets, even though SLI depends almost entirely on PCI Express in order to work.

Armed with the SLI bludgeon and a quiver bulging with marketing names like ActiveArmor, MediaShield, DASP, and QuickSync, NVIDIA has decided to cross over from the AMD market into the foreign, and much larger, territory of Intel-compatible chipsets. The nForce4 has not been without its growing pains, but it still dominates the enthusiast motherboard scene for the Athlon 64. Is the nForce4 SLI Intel Edition good enough to stand toe to toe with Intel's 925XE? We're about to find out.

What's new and what's not in the Intel Edition
If you read the paragraphs above and your eyes glazed over at the mention of an alien acronym, SLI, then you need to go read this, this, and maybe this, so you can get a feel for the technology. In a small and slightly shriveled nutshell, SLI allows one to drop two GeForce 6-class graphics cards into a single system and use them together to produce accelerated 3D graphics output on a single screen. SLI isn't particularly cheap or even really economical, but it can deliver higher performance, in certain situations, than any single-card solution currently available. That's the source of the nForce4 SLI's unique mojo.

The nForce4 SLI Intel Edition with a pair of GeForce 6800 Ultras

Beyond that, the nForce4 SLI Intel Edition has a host of other features to recommend it, many of them familiar from the AMD-oriented versions of the product. Those of you unfamiliar with the nForce4 basics may want to look over our review of the nForce4 Ultra in order to get up to speed.

NVIDIA has made a number of changes to the nForce4 on the road to Pentium compatibility, so this product might better be named nForce4.5. Let's review what's changed and what hasn't by doing a quick once-over on the nForce4 SLI Intel Edition's features list.

  • A real set of chips — The most obvious of the changes with the Intel Edition is that the nForce4 is now comprised of two chips rather than one. The single-chip approach works on the Athlon 64 because that processor has its own onboard memory controller, but on the Pentium 4, the chipset has to provide the memory controller. That chews up space on the chip and pushes basic I/O functions to another chip.

    NVIDIA has dubbed the nF4 Intel Edition's north bridge the SPP, for System Platform Processor. That's where the fancy high-bandwidth stuff happens. The nForce4 Intel Edition's south bridge has the fancy nickname of MCP, like the evil program in Tron that tried to kill everybody. In this case, though, MCP stands for Media and Communications Processor, which is appropriate, since the MCP handles audio and most forms of external I/O. The SPP is built using a 130nm fab process, while the humble MCP is fabbed on a 150nm process.

    A block diagram of the nForce4 SLI Intel Edition. Source: NVIDIA.

    The interconnect between these two chips is a HyperTransport link with a bitrate of 1.6GB/s. This isn't your Athlon 64's HyperTransport, though; in this implementation, the HT link only carries data between the north bridge and south bridge, so it's less important than the HT link between CPU and chipset on the Athlon 64. In fact, since the south bridge (or MCP) has no PCI Express links coming out of it, the chip-to-chip interconnect on the nForce4 Intel Edition should be plenty fast enough at this relatively low bitrate. Intel only uses a 2GB/s interconnect between its north and south bridges in the 925XE chipset, and its south bridge must handle some PCI-E connections.

  • 1066MHz front-side bus — The first order of business in any Pentium 4 chipset is a front-side bus, and the nForce4 Intel Edition has one capable of running at speeds up to 1066MHz, where only a handful of P4 Extreme Edition processors are likely to play. The nForce4 SLI will also support an 800MHz bus speed, which should be much more common.