nForce 4 SLI X16: Full Speed PCI Express
by Derek Wilson on August 8, 2005 1:56 PM EST- Posted in
- CPUs
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.
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PrinceGaz - Tuesday, August 9, 2005 - link
You can easily test to see if there is any performance difference between x8 and x16 PCIe with a standard nF4 SLI board. Just drop one card (ideally a 7800GTX) in the first graphics-card slot, and run tests with the paddle set to single-card mode. That gives you the PCIe x16 results. Now set the paddle to SLI mode and re-run the tests with the same single card. It will now be running at PCIe x8 and you can see if there is any drop in performance. Voila! :)Fluppeteer - Tuesday, August 9, 2005 - link
The thing about graphics slot bandwidth is that it's *always* much less thannative on-card bandwidth. Any game which is optimized to run quickly will,
therefore, do absolutely as much as possible out of on-card RAM. You'd be
unlikely to see much difference in a game between a 7800GTX on an 8 or 16-lane
slot (or even a 4-lane slot). If you want to see much difference, put in a
6200TC card which spends all its time using the bus.
There *is* a difference if you're sending lots of data backwards and forwards.
This tends to be true of Viewperf (and you've got a workstation card which is
trying to do some optimization, which is why the nForce4 Pro workstation chipset
supports this configuration), or - as mentioned - in GPGPU work. It might also
help for cards without an SLi connector, where the image (or some of it) gets
transferred across the PCI-e bus.
This chipset sounds like they've just taken an nForce4 Pro (2200+2050 combo)
and pulled one of the CPUs out. It does make my Tyan K8WE (NF4Pro-based dual
16-lane slots, dual Opteron 248s) look a bit of an expensive path to have taken,
even though I've got a few bandwidth advantages. Guess I'll have to save up
for some 275s so I don't look so silly. :-)
PrinceGaz - Tuesday, August 9, 2005 - link
I wasn't suggesting measuring the difference between x8 and x16 with a TC card, it was for people who are worried that there is some performance hit with current SLI setups running at x8 which this new chipset will solve. I'm well aware that performance suffers terribly if the card runs out of onboard memory, and was not suggesting that. Besides anyone with a TC card won't be running in SLI mode anyway so the x8 vs x16 issue is irrelevant there.I agree there is unlikely to be much difference between x8 and x16 in games but it would be nice to test it just to be sure. Any difference there is could be maximised by running tests at low resolutions (such as 640x480) as that will simulate what the effect would be of the x8 bus limitation on a faster graphics-card at higher resolutions. It's all about how many frames it can send over the bus to the card.
Actually my new box has a 6800GT in it and an X2 4400+ running at 2.6GHz, so I'll do some tests this evening then flick all the little switches (it's a DFI board) and re-run them, then report back with the results. I doubt there'll be much difference.
Fluppeteer - Tuesday, August 9, 2005 - link
Sorry, should've been clearer - I didn't mean to suggest abandwidth comparison test either, just to say that where
you don't see a difference with the 7800 you might with the
6200TC. Not that I'd expect all that many owners of this
chipset to be buying 6200s.
I'd be interested in the results of your experiment, but
you might also be interested in:
http://graphics.tomshardware.com/graphic/20041122/...">http://graphics.tomshardware.com/graphic/20041122/...
(which is the source of my assertions) - although not as many
games are tested as I'd thought I remembered. Still, the full
lane count makes a (minor) difference to Viewperf, but not
to (at least) Unreal Tournament.
Of course, this assumes that my statement about how much
data goes over the bus is correct. The same may not apply
to other applications - responsiveness in Photoshop, or
video playback (especially without GPU acceleration) at
high resolutions. Anyone who's made the mistake of running
a 2048x1536 display off a PCI card and then waited for
Windows to try to fade to grey around the "shutdown" box
(it locks the screen - chug... chug...) will have seen the
problem. But you need to be going some for 8 lanes not to
be enough.
It's true that you're more likely to see an effect at
640x480 - simulating the fill rate of a couple of
generations of graphics cards to come, at decent resolution.
The TH results really show when pre-7800 cards become fill
limited.
My understanding was that, in non-SLi mode, the second slot
works but in single-lane config. Is that right? I'd like to
see *that* benchmarked...
Ah, wonderful toys, even if we don't really need them. :-)
PrinceGaz - Tuesday, August 9, 2005 - link
Yes, when an nF4 SLI mobo is set to single-card mode, the second slot does run at x1 so it is still very useful assuming companies start making PCIe TV-tuner cards, soundcards, etc in the next year or two. Apparently Creative's new X-Fi will be PCI only at first which is lame beyond belief. The 250MB/s bi-directional bandwidth that a x1 PCIe link would give a graphics-card would have quite an impact I'm sure.Fluppeteer - Wednesday, August 10, 2005 - link
Re. the X-Fi, I don't see the bandwidth requirements needing morethan PCI (not that I know anything about sound); I'm sure they
can make a version with a PCI-e bridge chip once people start
having motherboards without PCI slots (which, given how long ISA
stuck around, will probably be in a while). If even the Ageia
cards are starting out as PCI, I'd not complain too much yet.
Apparently the X-Fi *is* 3.3V compatible, which at least means I
can stick it in a PCI-X slot. (For all the above claims about
PCI sticking around, my K8WE has all of *one* 5V 32-bit PCI
slot, and that's between the two PCI-Es. I hope Ageia works with
3.3V too...)
nserra - Tuesday, August 9, 2005 - link
"Obviously, Intel is our key processor technology partner and we are extremely familiar with their products. But we continue to look at the technology from AMD and if there is a unique advantage that we believe will benefit the customer, sure, we will look at it."jamori - Monday, August 8, 2005 - link
I'm curious as to whether or not they fixed the problem with displaying on two monitors without rebooting into non-SLI mode. I'm planning to buy a new motherboard this week, and am going with the ultra version instead of SLI for this reason alone.I figure I'll spend less on a motherboard and more on a videocard that will actually do what I want it to.
Doormat - Monday, August 8, 2005 - link
Anandtech, please make sure to test out the CPU Utilization when using the onboard Ethernet w/ ActiveArmor on production boards. I'd like to see if they revised that at all, since the CPU Utilization was so high on the current revision of the boards. In fact, most nVidia nForce Pro motherboards for Opterons dont use the included nVidia Ethernet, they use the Broadcom or some other chip because performance is so bad.Anemone - Monday, August 8, 2005 - link
Just cuz if you own the mobo a few years there will be things to stick in x1 and x4 slots I'm sure.Nice going Nvidia :)