Addressing the "you need 3GB vRAM" mantra for Surround

Matrices

Supreme [H]ardness
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Below you'll find a few benchmarks using Tri-SLI 580 at 3 x 1080p. I think it bears out my general conclusion: if you're OK with 2-4x MSAA and high-very high settings, there's no need to get 3 GB cards and 1.5 GB will suffice.

Even in the scenarios where you hit max vRAM limit, it's not choking performance, based on the FPS and my own observations watching the benchmarks. I don't know if this is because the engine is smart about it or because the extra data is offloaded to surplus RAM rather than the HDD.

There are a couple exceptions - 8x MSAA with Heaven benchmark will hard crash the machine, and according to [H], DAO2 with 8x MSAA chokes 1.5 GB vRAM - but that's outside the 2x to 4x MSAA parameters that I find sufficient. (Mainly because the IQ difference between 4 and 8x MSAA is next to meaningless, shader-heavy games have reduced the value of MSAA in the first place, and the next real IQ improvement - supersampling AA - isn't feasible at this resolution due to sheer horsepower requirements anyway).


DirectX 10 GAMER 1X @ Map: avalanche @ 0 5760 x 1080 AA 0x
==> Framerate [ Min: 59.34 Max: 115.81 Avg: 82.95 ]

DirectX 10 GAMER 1X @ Map: avalanche @ 0 5760 x 1080 AA 2x
==> Framerate [ Min: 44.75 Max: 68.35 Avg: 56.13 ]

DirectX 10 GAMER 1X @ Map: avalanche @ 0 5760 x 1080 AA 4x
 Framerate [ Min: 38.83 Max: 61.97 Avg: 49.32 ]


DirectX 10 ENTHUSIAST 1X @ Map: avalanche @ 0 5760 x 1080 AA 0x
==> Framerate [ Min: 47.68 Max: 73.60 Avg: 59.50 ]

DirectX 10 ENTHUSIAST 1X @ Map: avalanche @ 0 5760 x 1080 AA 2x
==> Framerate [ Min: 39.68 Max: 61.42 Avg: 50.83 ]

DirectX 10 ENTHUSIAST 1X @ Map: avalanche @ 0 5760 x 1080 AA 4x
==> Framerate [ Min: 36.82 Max: 59.75 Avg: 45.77 ] – 1512 MB max vRAM


JUST CAUSE 2 Max settings + 4x MSAA, 39.2 FPS AVG, 1112 MB max Vram


ARKHAM Max settings + normal physx + 4x MSAA: 117 FPS, 1527 MB max vRAM


HEAVEN 2.1 Regular settings + 16x AF + 4x MSAA: 53.6 FPS, 1522 MB max vRAM

BAD COMPANY 2 Max settings + 4x MSAA MP MAP HEAVY METAL: 1250 MB max RAM

Note: I didn't bother running with 3DVision because Nvidia software appears to impose a 2x AA limit when running 3D and Surround. It's not clear to me that it succeeds in doing so all the time, so it's an unnecessary variable. 3D does impose a 10-20% vRAM overhead, but that may or may not be canceled out by running at 2x AA and the fact that you can't notice aliasing as much with 3D on.
 
Has anyone else tried the same kinds of settings with both a pair of 1.5GB and a pair of 3GB (or 3-way) cards to see whether there are additional performance gains to be had if the extra VRAM were available? I've noticed this same sort of behavior with my GTX 570 SLI @ 2560x1600 in some titles where it bumps up against the limit but seems to have minimal impact on framerate, presumably due to the game engines swapping unused textures out as needed and streaming them back in once the player approaches an area with them again.

Trying to gauge whether I should jump to a pair of 1.5GB 580's, 3GB 580's, or stick with my 1280mb 570's for going 5760x1200 (or 3600x1920, depending on which I find I prefer). I'd be fine with sticking to 2x-4x MSAA or 8x CSAA, in fact I already do since I too find there to be minimal difference in most modern titles between the medium AA settings like those, and higher ones.

Thanks for the good info, Matrices.

EDIT: I found a user on the evga forums who was running gtx 470's experiencing essentially the same thing... I think I'll try my 570's with the new screens before thinking of any changes on the gpu end of things.
 
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I play @ 3240x1920 on my 2 480's. I notice I run of actual GPU power before mem as I start adding more bell and whistles. I usually run everything on high with 2x anti.
 

1 GB is not the same thing as 1.5 GB. When I posted my findings on Overclock.net, no one really disagreed, but someone did say that 1.5 GB was apparently the threshold for 3x 1080p because below that (GTX 570) others did see a hard vRAM bottleneck. Likewise, I imagine that at 3 x 1600p, anything below 2 GB would be a hard bottleneck.

It's disappointing that no site has run serious tests on any of this or interviewed developers to get the details of how all this works.
 
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I have a Surround setup using a Q6600 and two GTX 260s and realistically can play any game I like 6030 x 1200.

Typically don't use AA, so obviously take that with a grain of salt.

I think you can do whatever you want and have a nice experience. Sure my Tri-Fire computer runs things better, but I've bee really surprised with what my two measly 260s are capable of.
I think they tend to run framerates in the 40s but the play is smooth.
 
I play @ 3240x1920 on my 2 480's. I notice I run of actual GPU power before mem as I start adding more bell and whistles. I usually run everything on high with 2x anti.

GPU is still the rate limiting step on my 580SLI rig. I don't want less than 60fps so the AA and resolution are the first things I tinker with to optimise visual quality and framerate, which makes vRAM a moot issue.
 
Has anyone else tried the same kinds of settings with both a pair of 1.5GB and a pair of 3GB (or 3-way) cards to see whether there are additional performance gains to be had if the extra VRAM were available?
The thing with VRAM is that it can be hard to measure in framerates. I skimped on my last couple of GPUs (with a 256MB x1950pro, and then a 512MB 4850), so I know the problem well... You've either got enough memory or you don't, and once you don't, things degrade pretty fast. There's a very fine line between butter-smooth and nearly unplayable. And crossing it isn't always reflected in your framerate; you can stay clear 60fps while suffering through a couple of loading hitches every second.

So you might be just scraping by at the moment (10-20MB isn't a hell of a lot of breathing room...), but when you cross that limit, the difference is a lot more than a few FPS.

FWIW, 2xGTX580 3GB here, 2560x1600. Quick test of Crysis (4xAA) saw VRAM sitting just over 1600MB. With Rygel's texture pack it clears 2GB. From memory, Metro 2033 was close to the 2GB mark as well (though almost half of that is thanks to the depth of field effect...).
 
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