G'day
So, i'm just gonna call it SLI in this post because I buy Nvidia gpus.
Ok so my 2 questions are:
1. What does SLI double?
Like does it double the Vram, do the other gpus act as other cores? What actually happens?
2. What are all the problems tied in with SLI? I've heard that you have to chose profiles for certain games and that some games work worse with SLI?
Thanks.
SLI is the process of combining the performance of 2 or more Nvidia GPUs.
Now to your questions.
it does NOT double your VRAM. if you are running 2 780's for example in SLI you do NOT have 6GB of VRAM you still have 3GB.
now the Issues that come with SLI and Crossfire cause both have AMD and Nvidia have these issues are Scaling Issues, Screen Tearing, and potential graphical issues or the game will NOT even play at all (this is rare though but it happens) the issues can be bad enough that it can make a game unplayable or un-enjoyable.
Some games work better than others. the obvious case is that Nvidia titles have less issues with SLI than non-Nvidia optimized titles. and Nvidia Titles happen to run better with Nvidia Cards than AMD. Likewise with AMD optimized Titles.
Honestly You really should being going SLI or Crossfire for High Resolution gaming. 1440p, 1600p or 4K is where SLI or Crossfire would benefit the most.
Great post.
It should also be noted that some cards work better together than others. In mine, and quite a few other peoples' experience, the AMD 7870/R9 270X doesn't seem to do very well in Crossfire. Lots of issues with drivers, game comparability and performance. Other cards, like the GTX 760 or the R9 290 work very well together with minimal issues and very decent performance improvements.
Like Kat mentioned, dual GPU setups aren't usually recommended. I will only recommend a second GPU once you have exhausted all single card options and need more performance. IE you have a 780 Ti and it isn't enough.
1. What the driver usually does is called alternate-frame rendering. As the name implies, that means each GPU works on alternating frames, at the same time. To do this, each GPU has an exact duplicate of whatever is in VRAM (which is what the bridge is for). That is, if you have 2 2GB cards stacked together, you still effectively only have 2GB.
Ideally, this would double the framerate of the game. In practice, most multi-GPU setups push some bottleneck or another onto the CPU and video driver, so you very rarely get that much. 75-90% scaling is typical, if you're playing a game that actually supports it.
Other than sharing duplicates of the same VRAM, the GPUs work almost completely independent of each other.
2. The reason that not all games can support multi-GPU setups is that game developers have no direct control over it. Most games that properly support it are the ones with profiles, which are generally made by Nvidia or AMD. Some games can work without a profile, but you can't really expect that they will. This means smaller games, like the Wargame series, don't support it at all, and can actually lose performance if you have SLi or Crossfire active.
Thanks for the replies! Ok well I do actually have a 780ti and next year i will be going for 4k once proper 4k at 60hz with those good panels (what are the called again? TN? or is that the bad one? come out. SO instead should I just get 1 card with 6GBs of Vram? Because i'm pretty sure the Vram is the only bottleneck. In that case would 1 Titan be better than 780ti in SLI? Within reason. Thanks.
TN has faster refresh rates and can display more images per second than IPS/PLS(samsung's IPS). These do not have to color reproduction of IPS displays, but are great for gamers who really want the smoothest gameplay experience(depending on the panel, ofc)
IPS usually has a 5ms or more response time, at 60hz. 60hz is usually enough for most people, and IPS allows for really nice viewing angles as well as much, much better color reproduction. Great for content editing, and alright for gaming.
Oh ok thanks, I'll get a IPS one then :)
If you want good framerates on high settings at 4k at this point, you need 2 top-end GPUs. Don't bother with a Titan, for anything, really. SLi Titan or 780ti, or crossfire 290 or 290X. Anything less and you'll be sacrificing quite a bit of performance. All of those GPUs have plenty of memory for all but the most demanding games at 4k, but you really do need the extra horsepower.
You said don't use a Titan and then you said I should use a Titan, also why not if not?
It's just that a 780ti is both faster and cheaper. The only thing the Titan has over a 780ti is more double-precision power. It has no bearing on games.
Well if you have a 780ti already, just make sure your motherboard and power supply can support SLI. Then, just add another 780ti.
This.
But if you don't have a 780 Ti, I'd pick up a two 290x's or a 295x2. On low to medium settings the AMD cards vastly outperform the 780 Ti's at 4k, and when you increase the graphical fidelity to high or medium the AMD cards are still better but not by such a huge margin. Some games like bioshock infinite and also probably Skyrim would run better on the 780 Ti's though.
Also I'm not sure if the 780 Ti's perform so poorly due to 3 GB of VRAM compared to the 4 GB on the 290x's, or if it's the 384 bit memory bus compared to the 512 bit one, or both. I can't be sure if using two Titan Blacks would give you performance that is much more competitive with two 290x's (ignoring price).