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PhysX & SLI, a 3:d GPU dedicatet to PhysX?

Last response: in Graphics & Displays
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January 10, 2012 5:53:30 PM

Have som software and hardware questions I want to clear out. All details is in my profil but heres the 2 relevante ones:

MB: ASUS Sabertooth X58 s1366
GPU: TWO MSI N460GTX HAWK 1GB GDDR5 in 2x16x SLI mode

Is wondering if insert a third GPU and dedicate that to PhysX is possible and if that choice would generate more data/graphic raw power advantage than what that would slow down the graphic system in form of bus speed? My MB supports 2x16x SLI and/or 2x16x or 2x8x1 Crossfire. It has 3 PCIe x16 slots, when using slot number 2 the bus speed of slot number 3 automaticly slows down to x1 in Crossfire mode (dont support 3-channel SLI).

Question # 1: Is it even possible to install a third NVIDIA GPU in slot 3 when running 2-channel SLI?
Question # 2: If that is possible, would the bus speed go down to 2x8x SLI + 1x PCIe PhysX dedicated NVIDIA GPU (slot 1 & 2 bus speed is 8x and slot 3 bus speed is 1x)?
Question # 3: Can I then install a different NVIDIA GPU than those two I have, like a GTS 450 or another slower card then my N460GTX, and totally dedicate that GPU to PhysX computing? Or must I have the same card as I use as SLI?
Question # 4: Would this configuration give me more graphic power in total even that the bus speed will slow down to half the speed?

Would be happy if you can help me with this!
a b Î Nvidia
January 10, 2012 6:11:10 PM

1) yes
2) yes
3) yes
4) no

Basically at 1x, only the absolutely slowest of GPUs will be able to run normally. I have a GT 240 in a 4x slot and it can only use up to 82% usage.

Anyway, dual 460s should have the power to run PhysX in almost any game at highest settings. The only real exception would be the two Batman games, but you could still do it at normal.

Also, http://en.wikipedia.org/wiki/PhysX#PhysX_in_video_games
January 10, 2012 6:11:45 PM

The real question to ask is what Physx or how many Physx games do you play?
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January 10, 2012 6:22:49 PM

You need the same card for SLI, if its overclocked, the clock will get bumped down to that of the slower card.

Other than that, I dont have an answer to your question. Check nvidias site:
http://www.slizone.com/object/sli_physx.html

Wow, seems like I was wrong, you can take a weaker gpu and use it for physix. cool stuff!

But what can two 460s not already handle?
January 10, 2012 8:04:40 PM

Thank you all! Its super to have someone to ask when it comes to things you never thought about before. Yes my GPUs in 16x SLI IS very good, got 6948 points (if I dont remember wrong) in 3DMark 2011 free verision. Have not yet started to OC the system, just came to my mind that PhysX is a important tool in those programs/games that use it.
a b Î Nvidia
January 10, 2012 8:20:24 PM

If you're interested, about OCing I just wrote a beginner's guide on my blog. You can also find it here on Tom's in the Overclocking section.
a b Î Nvidia
January 10, 2012 9:02:46 PM

The problem with physx when there is no dedicated card in a two or three way AFR sli system is unbalanced load and reduced over all fps. Adding a dedicated card will balance the load in sli and enable better performance in physx titles. Second you will be able to run a third cuda client instead of only two.

I have run dedicated physx cards thought out my time and have experimented on several cards. 8400gs before requirements had changed (horribly weak), I have tested a 8600gt in dedicated physx and it wasn't all that great. Then I moved to a 8800gt for dedicated physx.

The physical slot must be able to fit 16x cards however they do not have to run at 16x speed to see worth while gains. 4x in my testing is no bottleneck for a dedicated card however never tested at 1x.

You can run it however 1x might not be enough but who know when pci was good enough for an Ageia PPU (physx card) that is on par with a 8600gt in physx.

I suggest that you look for only a single slot card and that you avoid low end Fermi era cards due to weak overall 32bit single precision floating point performance which is what most applications depend on. A GT240 or a single slot 8800/9800gt if you can find them. If all else look for a GTS450 eco from zotac or the gts 450 from sparkle that does not need a 6pin power connector.
a b Î Nvidia
January 11, 2012 1:53:47 PM

Max1s said:
But most games dont even use physix. There are only a few (in my opinion) good games with physix support.

http://developer.nvidia.com/physx-games


That list is very misleading. Only a few of those games use accelerated PhysX. Most of them use it as a regular old physics engine, no different than Havok for example.

This list is the games that use acceleration:
http://en.wikipedia.org/wiki/PhysX#PhysX_in_video_games

The highlights, IMO:
Batman 1/2
Metro 2033
Mirror's Edge
Cryostasis
Mafia 2

Sacred 2, Dark Void, and Darkest of Days look decent but I haven't tried them myself.
January 11, 2012 2:06:56 PM

Yeah, it did look a little long. But I dont really think physix is worth it, since I dont play and dont think I will be playing any of those games.
a b Î Nvidia
January 11, 2012 2:12:52 PM

Meh, I spent $65 on a GT 240 and it is a cool feature. Not really worth it for most people, true, but the OP is interested.
January 11, 2012 3:36:00 PM

Yeah I guess for that price its cool.
So if you do have a slower GPU dedicated to phyisx, does it just let the other GPU(s) take more of the pure graphics load and your fps goes up?
a b Î Nvidia
January 11, 2012 3:39:38 PM

Graphics are 100% on the main GPUs.

The PhysX GPU only handles the special PhysX features like enhanced water, particles, cloth, smoke, etc. If there are a *** load of PhysX things going on and the PhysX card is maxed out, you can lose some framerate, but otherwise the PhysX card shouldn't impact FPS at all.
January 11, 2012 3:41:43 PM

But lets say you have a GTX 260, and then add a GTS 240 for physx, the framerate on the game goes up right? What about non-physix games?
a b Î Nvidia
January 11, 2012 3:46:23 PM

If you were running PhysX on the GTS 260, then yes adding the dedicated card would improve framerates a lot.

In non PhysX games it won't change a thing.

You might want to check this site out: http://physxinfo.com/
January 11, 2012 3:47:58 PM

Woah wait I went to your blog to take a look at the sexy sig in your thumbnail, and you have AMD cards WITH nvidia cards for physx? Can you do that?

EDIT: I just read the blog thing about that, thats really cool, too bad only physx games are helped.
a b Î Nvidia
January 11, 2012 4:07:59 PM

Max1s said:
Woah wait I went to your blog to take a look at the sexy sig in your thumbnail, and you have AMD cards WITH nvidia cards for physx? Can you do that?

EDIT: I just read the blog thing about that, thats really cool, too bad only physx games are helped.


:D 
a b Î Nvidia
January 11, 2012 4:35:05 PM

wolfram23 said:
That list is very misleading. Only a few of those games use accelerated PhysX. Most of them use it as a regular old physics engine, no different than Havok for example.

This list is the games that use acceleration:
http://en.wikipedia.org/wiki/PhysX#PhysX_in_video_games

The highlights, IMO:
Batman 1/2
Metro 2033
Mirror's Edge
Cryostasis
Mafia 2

Sacred 2, Dark Void, and Darkest of Days look decent but I haven't tried them myself.


I've played two of those games that you haven't tested and Sacred 2 isn't much when it comes to physx but it does show time to time. Dark Void however often needs a bit of a crutch to keep the fps up.
January 11, 2012 5:14:34 PM

Personally I'm only curious about Mafia 2 and doing some interior decorating with a Tommygun. :-)
a b Î Nvidia
January 11, 2012 5:47:13 PM

Max1s said:
Personally I'm only curious about Mafia 2 and doing some interior decorating with a Tommygun. :-)


I play Mafia 2 on my setup, 52% load on my 8800gt as a dedicated physx card. 2x gtx280 in sli + dedicated 8800gt.
a b Î Nvidia
January 11, 2012 5:49:22 PM

Mafia 2 uses really good PhysX destruction and particle effects. There's one part where you're on a big machine gun mounted in a window and have to blast a couple cars (and people) to pieces. So awesome. There's another part where you're in a bar setting and have a huge shoot out, lots of walls get blown apart there. Especially one of those fog-glass window/walls.
January 11, 2012 6:06:45 PM

Lol, one day......
!