Introduction

Ever since its launch in the fall of last year, nForce 4 has brought us SLI capability. Configurations for PCI Express slots in nForce 4 SLI motherboards must be selected by using a paddle that can be flipped to allow for either 2 x8 connections or full bandwidth for one with the other disabled. There is added flexibility on an nForce 4 SLI motherboard, but this flexibility comes with some limitations. Today, NVIDIA sheds the shackles of the paddle selector and limited bandwidth with the new nForce 4 SLI X16 chipset.



In addition to the increased bandwidth and ease of use come quite a few extra niceties. Boards based on nForce 4 SLI X16 will have more I/O options on top of the added PCI Express bandwidth. The introduction of a new enthusiast part will also push prices down on existing products and NVIDIA will begin selling its current nForce4 SLI solution at mainstream prices. Aside from cheaper being better, this should increase adoption of the SLI platform giving the mainstream user some reason to care about SLI. With this also comes value for options like 6600 and 6200 SLI. Everything seems to be coming up roses for NVIDIA's dual GPU business right now with ATI's Crossfire still waiting in the wings.

With this introduction also comes quite a surprise from Dell. NVIDIA will be supplying core logic to the previously Intel-only volume computer manufacturer, making nForce4 SLI X16 the first non-Intel chipset for dudes to get in their Dells. This is quite a big announcement and will really help to boost NVIDIA's already successful chipset business. This announcement also gives some glimmer of hope for Dell as non-Intel hardware on the motherboard may mean that Dell is capable of making good decisions in the processor department as well. While it is unlikely that we will see AMD based Dell systems anytime soon, it's nice to know that the thin line between volume discounts and unfair business practices is clear enough to allow Dell to make the right choice for performance once in a while. At least, now one of their chipset vendors supports AMD as well as Intel.

Unfortunately, we don't yet have a board to test for performance numbers on the new configuration, but that won't stop us from talking about what's new under the hood.

The New AMD and Intel Chipsets

The upgrade to nForce4 SLI X16 is more of an upgrade than an overhaul. This solution expands NVIDIA's core logic solution to two chips rather than one. The current nForce4 MCP will act as the southbridge and will be connected to the new AMD nForce4 System Platform Processor (SPP) via its HyperTransport link (usually connected to the processor). This gives 8GB/s bandwidth between the AMD MCP and SPP. Added latency over the HT link shouldn't be very high and we don't suspect that it will have an impact on anything. The SPP and MCP each provide x16 PCI Express links along with a few other choice features.

As the Intel core logic solution already incorporates an SPP, the upgrade for the Intel nForce4 SLI X16 is even simpler. Since the MCP included on the current Intel chipsets simply has its PCI Express lanes disabled; enabling them is all that NVIDIA needs to do. The total number of available PCI Express lanes on Intel nForce4 SLI X16 based systems comes to 40 after the SPP and MCP are added together. These lanes can be divided up into 9 different slots. AMD based systems will offer 38 lanes over up to 7 slots. This means that we could see a bunch of x1 or x2 slots, but since PCI Express cards can plug into larger slots and this solution has lanes to spare, we'd like to see some larger connectors on these consumer motherboards. There aren't any widely available parts to make full use of the bandwidth now, but motherboards that cost upwards of $200 should be somewhat future proof and flexible.

NVIDIA states that motherboards shipping with the nForce4 SLI X16 chipset will generally have all the enthusiast bells and whistles like dual gigabit network connections and 6 to 8 SATA ports. Supporting all these options alongside up to 40 PCI Express lanes (38 for AMD systems) and 5 PCI slots, these new motherboards will cater to almost workstation level I/O needs. For example configurations of Intel and AMD solutions, take a look at these block diagrams provided by NVIDIA.





These configurations can vary depending on the manufacturer of the motherboard.

Final Words

The first motherboards are only available from Dell, and other vendors will be bringing out products shortly. NVIDIA is shipping chips now, so it shouldn't be too long before we are able to buy an SLI X16 based board. Normally, we would lament the break in NVIDIA's recent trend of announcing a product with immediate broad availability, but if that's what it takes for NVIDIA to get a deal with Dell, then more power to them. Getting the SLI X16 into the new XPS 600 is quite a big deal for NVIDIA.

NVIDIA is touting the added bandwidth as a performance increasing factor for the future. They acknowledge that current games don't see much benefit from the added bandwidth, but stand firmly behind the assertion that future games designed for PCI Express and SLI will take advantage of the increased bandwidth offered. We certainly aren't expecting to see any major gains under current titles, but we will have to wait until we get our hands on a board to play with before we can say for sure what we think of the performance.

We did take a couple of shots at comparing workstation class hardware to current nForce 4 SLI (nForce Professional enables 2 full x16 PCI Express connections with 2 processors), but due to the processor and memory configuration difference, we couldn't devise a fair test that could narrow down the impact of PCI Express bandwidth on real world games. Hopefully, we will have an SLI X16 board in our labs sooner rather than later.

There are no downsides to the convenience and market impact factors of this launch. On the high end, not having to flip a paddle is a welcome change. The added configuration options that motherboard makers will have for PCI Express slots can only help speed adoption. As motherboards based on the SLI X16 chipset will come in at current high end prices, the current SLI boards will fall in price and mainstream users will find little reason not to grab an SLI based system over the NF4 Ultra. More people with SLI systems means more impact from things like budget and mainstream GPUs supporting SLI. Here's the new price structure for NVIDIA based motherboards as NVIDIA sees it.



This is also a preemptive blow to ATI's Crossfire. With Crossfire motherboards not offering more than 2 x8 slots and many manufacturers going with the paddle design rather than ATI's recommended ICs for auto configuration, the new ATI enthusiast board will be stuck competing with a now mainstream product from NVIDIA. To be sure, the Crossfire motherboards are very good performers, but with this new option from NVIDIA and the price drop in current SLI products, ATI will have an even harder time getting their motherboards to end users.

We also see some possibilities for the GPGPU crowd with this addition of bandwidth to SLI configurations. This setup does more than just make it easier to move data around on each card. GPGPU stands for "General-Purpose Computation on Graphics Hardware" and with this setup, there is more than twice as much bandwidth dedicated to graphics as there is to system RAM in an AMD system with DDR 400. Depending on the latency, this opens up quite a number of possibilities for using the storage space available on graphics cards when they aren't in use. If some program (or even Windows itself) decided to treat unused graphics RAM as a separate memory node, we could see a total theoretical memory bandwidth of well over 20 GB/sec. Since system busses don't get guaranteed latencies, we would have to expect something like this to only benefit very high bandwidth stream processing. There was some talk at NVIDIA about GPGPU projects that they have under wraps, but they didn't give us any indication of what they are looking at doing right now.

In the end, even if performance impact isn't great (and even if NVIDIA's promised future performance benefits never materialize), this launch is a very good thing. Pushing prices on SLI systems down to more affordable levels and offering the potential for more PCI Express expansion slots (each with higer bandwidth) is definitely welcome. This is not the kind of solution that will entice current nForce4 SLI users to upgrade and the verdict is still out on whether or not there will be a real world performance difference, but the existance of the nForce4 SLI X16 solidifies NVIDIA's position in the core logic market and helps to push prices down across the board.