If say you need more than 1.5GB or RAM and you have a 1.5GB 580 and the 780, only the 780 will kick in - even if you select them both as active compute cards. adding a 780 to your current system will be working fine, with you having the option to render with either the 580 (actually the fastest single GPU GTX in VRay RT before the 780 and Titan) or the 780 or both simultaneously - given the scene 'fits' in both's VRam individually. On the 'pro' side, you don't need to pair them with identical models as you do with SLI/CFX: i.e. Each one has half of the RAM 'advertized' for individual and exclusive use, and if an application doesn't support SLI/CFX (like 3DS Max or Maya viewports as of 2014 versions for example), you are only using 1x GPU and half the ram. Just doesn't.Įach GPU needs to have all the assets available in its own VRam buffer to get started.ĭual GPU cards, like the GTX 690 or the Radeon 7990 are often advertized as '4GB' and '6GB' cards, but this is marketing bluntly lying: those are 2x individual GPUs on a single PCB SLI/Crossfired together, with one being the primary and the other being the secondary. Not for games either - doesn't matter if you SLI or not.

Not for VRay RT, not for any other progressive rendering or GPGPU application. It is certain that VRAM in cards doesn't add up. I hope so since I will keep my 2x GTX 580 3gb for a while and make some sequences. It will be way faster on never cards like GTX 780, but GTX 580 might keep up okay. I think, and I'am pretty shure that Vray 3.0 will change these things quite drastically. No Vray RT, but hopefully it will compare pretty good with iRay or Octane.

Tom's Hardware has very GPU renderengine benchmarks that is really good. 6gb memory on the GPU though is a very neat improvement. Unfortunately the speed improvement hasn't been that great two generations later (from GTX 580 to 780) when you render with physically accurate render engines. So my projects will be a little 'easier' on that part and I have to think twice when i model, but It's okay since I'am still a architect student. I have 2 GTX 580 3gb and think that i will be quite limited with the amount of ram.

Vray benchmark list