Its interesting. Their 4 way SLI never really took off because the GPUs on the cards used (7950s) were slower than the 7900. One card was a bit worse than two 7900s.
Most SLI games apparently use alternate frame rendering, but in DirectX 9 you're only allowed to render three frames ahead, so it didn't work. Thus support was bad.
If you look carefully at the chipset diagram you'll see that the third PCI-Expressx16 slot is version 1, not 2, meaning it has half the bandwidth of the others. As nothing really uses PCI-E 2.0 to its full extent yet and they are still using seperate SLI connectors I don't see that as being a problem. If I remember right there's a 790i coming out soon with three 2.0 slots on it.
Three way SLI only works under vista at the moment, but as it only needs a three frame advance it should work on XP.
The new and exiting G92 based cards (that I posted about recently) only have one SLI connector, so they won't work in three way. This gives a reason to keep the old GTX and Ultra in the lineup I guess.
The summary is that, unless you're doing something unusual or have too much money, it doesn't look worth it. Maybe next generation...
Actually, I suspect this is going to be a monumental waste of money. SLI gains you very little in the general case anyway, due to games needing to be optimised for it (and very few games being GPU limited on even a single high-end card). And I'd bet that even those games that are optimised, aren't optimised in a general way, but specifically for 2 card set-ups.
Submitted by AggroBoy on Tue, 2007-12-18 11:08
Indeed, its probably not worth it unless you know the games you play support it and you have a ridiculously high res (like 2560x1600) monitor...
One even closer inspection, the two PCI-E 2.0 16x slots come off the nForce 200 chip. Fine. No problem. But the nForce 200 chip is connected to the 780i SPP (~=northbridge) by 16 PCI-E lanes.
Um. 16 lanes, in, 32 out. I see a problem.
So assuming you want your graphics cards to talk to something other than each other with half of their bandwidth, you have a problem. If they do something really quite clever and send all the info for SLI to the 200 chip and then duplicate it to each card then you'll be getting the performance you expect. If not, you'll be getting the equivilant of PCI-E 2 x8 per card with two plugged in, which is equal to PCI-E 1 x16.
So it probably doesn't matter. But it doesn't look like you'll be getting the bandwidth advertised. Not that it'll make any difference, GPUs don't really benefit that much from the extra bandwidth.
Comments
Its interesting. Their 4 way SLI never really took off because the GPUs on the cards used (7950s) were slower than the 7900. One card was a bit worse than two 7900s.
Most SLI games apparently use alternate frame rendering, but in DirectX 9 you're only allowed to render three frames ahead, so it didn't work. Thus support was bad.
If you look carefully at the chipset diagram you'll see that the third PCI-Expressx16 slot is version 1, not 2, meaning it has half the bandwidth of the others. As nothing really uses PCI-E 2.0 to its full extent yet and they are still using seperate SLI connectors I don't see that as being a problem. If I remember right there's a 790i coming out soon with three 2.0 slots on it.
Three way SLI only works under vista at the moment, but as it only needs a three frame advance it should work on XP.
The new and exiting G92 based cards (that I posted about recently) only have one SLI connector, so they won't work in three way. This gives a reason to keep the old GTX and Ultra in the lineup I guess.
The summary is that, unless you're doing something unusual or have too much money, it doesn't look worth it. Maybe next generation...
Review here
Did someone call my name? Where do I sign up? :)
Actually, I suspect this is going to be a monumental waste of money. SLI gains you very little in the general case anyway, due to games needing to be optimised for it (and very few games being GPU limited on even a single high-end card). And I'd bet that even those games that are optimised, aren't optimised in a general way, but specifically for 2 card set-ups.
Indeed, its probably not worth it unless you know the games you play support it and you have a ridiculously high res (like 2560x1600) monitor...
One even closer inspection, the two PCI-E 2.0 16x slots come off the nForce 200 chip. Fine. No problem. But the nForce 200 chip is connected to the 780i SPP (~=northbridge) by 16 PCI-E lanes.
Um. 16 lanes, in, 32 out. I see a problem.
So assuming you want your graphics cards to talk to something other than each other with half of their bandwidth, you have a problem. If they do something really quite clever and send all the info for SLI to the 200 chip and then duplicate it to each card then you'll be getting the performance you expect. If not, you'll be getting the equivilant of PCI-E 2 x8 per card with two plugged in, which is equal to PCI-E 1 x16.
So it probably doesn't matter. But it doesn't look like you'll be getting the bandwidth advertised. Not that it'll make any difference, GPUs don't really benefit that much from the extra bandwidth.