nForce 4 SLI X16: Full Speed PCI Express
by Derek Wilson on August 8, 2005 1:56 PM EST- Posted in
- CPUs
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.
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akugami - Monday, August 8, 2005 - link
This will boost video graphics performance as much as when 8x AGP came out over the then cutting edge 4x AGP. Which is to say slim to none. As others have stated, there is no known graphics card capable of fully utilizing the 8x AGP bus much less 16x PCI-Express bus. The Geforce 7800 doesn't come in AGP flavors so we don't know if it has a significant performance difference between 4x and 8x AGP.JarredWalton - Monday, August 8, 2005 - link
A few thoughts about the bandwidth increases now offered with the new chipset. First, for transfers from system RAM to the GPUs, this is completely useless. I also have to wonder what the link between the MCP and SPP is - it would have to have 8 GB/s of bandwidth to make the second X16 slot the same speed as the primary SPP slot. Hmmmm.... most I've heard of for a NB to SB interconnect is about 1 GB/s. Two HyperTransport channels running at 1000 MHz would provide enough bandwidth, but I seriously doubt that's present.Now, even if the NB to SB connection were fast enough, dual-channel PC3200 DDR only offers 6.4 GB/s of bandwidth - less than that of a single X16 slot. So SATA controllers sitting on X4 connections combined with two GPUs on X16 connections will now be possible, but the actual performance probably wouldn't be any different than SATA controllers on an X2 connection with two GPUs on X8 connections. Maybe we'll get quad-channel DDR2-667 RAM with socket M2 to make this a realizable performance boost? (/sarcasm)
There is a use case for it, though: GPGPU for one, and potentially SLI without the extra connector. Board to board SLI transfers over the internal X16 should be at least as fast as the proprietary connector I'd think. That last one is especially interesting, I think. If current SLI takes an X16 channel and breaks it into two X8 channels, how about a board with four X8 connections and four physical X16 slots for quad-GPU SLI? It wouldn't surprise me at all to find that NVIDIA has a team working on that exact project.
As the article states, the biggest deal about this launch for gamers is that prices will drop on SLI boards. Maybe then I'll be able to stomach recommending SLI for a mid-range system. The even bigger deal for NVIDIA is that they now have an "in" with Dell. THAT is freaking huge! I don't think Dell actually sells that many XPS systems, but then I don't think that many Intel SLI setups have been purchased as a whole. Dell has marketing power, and they WILL find ways to convince people to buy Intel SLI PCs.
ceefka - Tuesday, August 9, 2005 - link
4 graphics cards? Looks like the PC is turning into a gaming console and losing its general purpose, unless you're a stock broker maybe ;-)Having this abundance of PCI-E lanes looks like a step to abandon PCI(-X). The nF4 boards have issues with professional soundcards on the PCI-bus. It is a pity all these gadgets and extra performance have downgraded the PCI-bus instead of enhancing it.
I believe it is time for cardmanufactureres to develop more PCI-E based cards. It seems like chipset manufacturers aren't willing to spend the time to preserve good bandwith for the old PCI-bus.
ChiefNutz - Monday, August 8, 2005 - link
Nvidia Graphic cards communicate through their "crossbar" on the top of the cards, so, even having just 1 HT link between SB & NB wouldn't be that big of a deal. I don't think that it would saturate the HT link either, due to the crossbar. But this setup would be nice in a system if they got rid of the 16x crap and just gave you the straight channels like the 2200pro and 2250, like a 8x or 2 4x slots like that.What I really want to know is will they now support raid 5 on a non NForce-Pro AMD system?? Intel edition has it and so does the 2200pro? where is the NON-ECC love!
JarredWalton - Monday, August 8, 2005 - link
Yes, they have their crossbar controller, but they still get information from the CPU and main memory. If you ignore the GPU to CPU/RAM via PCIe bus communications, then there is no difference whatsoever between SLI X8 and SLI X16. (Which is likely the case anyway.)RAID 5 appears to be coming with the nForce4 SLI X16 chipsets to both platforms. We just neglected to mention it:
afrost - Monday, August 8, 2005 - link
So now nforce boards will have two really hot chips that need loud little fans or elaborate heat pipes? I hope that with this new generation of nforce chips they figure out a way to cut down some of the heat output. The nForce 3 was perfectly fine but the 4 gets toasty.This is one of the main reason that I am looking forward to the ATI boards....I like passive chipset coolers.
Anton74 - Monday, August 8, 2005 - link
Perhaps now that it is a 2 chip solution rather than 1, each of the chips will run a bit cooler than if they were combined, hopefully allowing for simple passive cooling with good (aftermarket) heatsinks like that blue Zalman one, the ZM-NB47J. As long as they don't put those chips in un-strategic places...Gerbil333 - Tuesday, August 9, 2005 - link
That was my first thought when I read this. The current nF4 chips run way too hot. I really hope the new two chip design runs cooler.virtualrain - Monday, August 8, 2005 - link
Doesn't this solution completely do away with the need to either open the case and flip the switch to enable SLI or select it electronically (i.e. ASUS A8N-SLI Premium) and reboot?If so, that's a positive move even if there is no performance gain.
One of the appeals of ATI's crossfire solution is the expanded flexibility and ease-of-use. I think this even's that part of the playing field somewhat.
Calin - Tuesday, August 9, 2005 - link
As I remember, old NVIDIA SLI had that switch to distribute the PCI-E lines in 1x16 (a single usable slot) or 2x8 (two usable slots). There might have been some kind of extra connections to have a single x16 slot and one 4x slot (20 PCI-E lines used) or two x8 slots (16 PCI-E lines used, and 4 unused).It would be great to be able to change the SLI/non-SLI configuration from drivers.