About Nvidia SLI

[leehwang]

When I wrote my last thread, I could reconize many of you are using SLI system. Maybe I will buy a new system in this month so I am agonizing about SLI system. I decided to buy GTX 460 model and after 2 years later, I would
try SLI. For now, I should spend more money for 600W POWER and SLI Mainboard. It seems I need about $35~40 more.

But I am worry about SLI's performance because someone told me SLI has bugs in UDK. I would like to ask to people who are using SLI system.
Are you satisfied with SLI? If I use 460SLI, Could I feel much better performanc in UDK?

[micahpharoh]

I use SLI and it's a great boost to most games, including the UDK. However, there is a bug that makes it impossible for me to use the UDK Editor with SLI enabled. You can selectively disable SLI, though. So I have it on, just not for the UDK. That's the unfortunate part, though. The UDK counts as one big piece of hardware, whether you're in the editor or in game, so you can't disable SLI for one and not the other.

I hope this helps. It sounds like if you're going to wait 2 more years anyways they might have fixed it by then.

[Nawrot]

Get 650W, because PSU lose power in time its about 10% per year, and 600W is right on the edge for 460SLI. I have 650W with 470in SLI and it causes instability in most demanding games, simply there is not enough juice. But for 460's 650W should be optimal.

Limit FPS in UDK to 60, when i removed limiter UDK got a bit extreme and ruthless, and keept 100% load no matter what (as expected) this resulted of faster boiling of cards and that weak PSU issue surfaced.

Be very carefull about type of motherboard. 460's use 2 slots (double size cards), because nowadays CPU are quite big, and first 2 slots (closest to CPU) usually are taken by CPU or some logic chipset. This leaves 5 free slots for cards, so last one (460's are double sized) extends beyond motherboard. Your PC box should allow mounting card there, or prepare for some cutting.

You want put cards in first and last slot leaving middle empty, because of extreme overheating when you put them sandwitched. Your cards run at lower temp than mine, so you may get chance (but at cost of higher fan noise). Mine when sandwitched overheated to 100C in matter of minute or two, so i had no choice and needed to leave middle empty. Now I call total marketing BS when they advertise 3 way SLI with 470's, without moding those cards cooling its impossible.

Ps. there are only 2 games i know that can get mine to 100% load: UDK without 60fps sync, and Oblivion with all details maxed, in some open places its gets demanding.

[Mougli]

Last time I tried SLI (a few years ago), you couldn't have a multi-monitor desktop while SLI is enabled which made the whole thing pointless, because UnrealEd on a single screen, well...

I did not measure the performance gain at the time, but in my opinion, even if you have only one screen, it's not worth the money.

(And I haven't seen any game dev studio using SLI/Crossfire-enabled computers).

[micahpharoh]

@Mougli SLI doesn't have the dual screen limitation anymore. That's been fixed for at least 2 years. I've been running dual screen with SLI for at least a year myself.

@Nawrot I agree, the cards get really hot when they're next to each other, but some mobos are made so you can't set it up any other way. If the two PCI slots that you need are right next to each other there's nothing you can do about it. I wouldn't want to plug one of my cards into the 3rd PCI slot that runs at a slower speed because that would limit both cards.

[Nawrot]

@Mougli SLI doesn't have the dual screen limitation anymore. That's been fixed for at least 2 years. I've been running dual screen with SLI for at least a year myself.

@Nawrot I agree, the cards get really hot when they're next to each other, but some mobos are made so you can't set it up any other way. If the two PCI slots that you need are right next to each other there's nothing you can do about it. I wouldn't want to plug one of my cards into the 3rd PCI slot that runs at a slower speed because that would limit both cards.

That is why I always write about sandwitched cards here (to warn people), and that one should research into it (ie. how slots on mobo are placed) before purchase.

Best way is if slots have speeds: 16x .. 8x .. 16x, then you put cards into first and 3rd, so there is empty space, but most (if not all) mobos have 16x 16x 8x, so either you use 2 fast slots and boil cards or you leave space and are forced to use slower x slot. Also some PC cases do not have space for double card in last slot. And putting second SLI in slower port does not limit speed that much, difference is 5-10% at most, but its exactly what you gain from going 460SLI to 470SLI. So its cheaper to get both 460 in 16x speed slots than two 470s in 16x and 8x ones due to overheating and lame mobo layout.

PS. For gaming i usually use second card for physx, there are no games that need power of SLI, besides Oblivion in 3d mode (that thing can devour all power it gets).

[leehwang]

Thank you everybody. I bought hexacore system of AMD with ZOTAC 460. And I didn't know that PSU lose power in time its about 10% per year. But I bought 600W Power Already. I am worry about it because it can cause the problem which U said. Anyway those were really good advices. Thank you all.

[Nawrot]

It should be just enough for sli 460, they use far less power than 470s. Just do not play Oblivion in SLI when you burn DVDS.