Stacked VRAM Possible in CF/SLI for Low level API's

Stacked VRAM possible for Low level API's

| Source: Robert Hallock Author: Mark Campbell

Stacked VRAM possible for Low level API's

It is well known that VRAM currently does not stack when using a Multi-GPU configuration, instead the memory on both GPUs must have a copy of the same data as each frame is alternated between the GPUs.

Robert Hallock, an AMD Representative, has tweeted that with the advent of low level API's like AMD's Mantle and Microsoft's DirectX 12 that 2 GPUs can act like a single larger GPU with stacked GPU memory if the correct optimisations are made.

(in the future this R9 295X2 may act like an 8GB GPU)

"Mantle is the first graphics API to transcend this behavior and allow that much-needed explicit control. For example, you could do split-frame rendering with each GPU ad its respective framebuffer handling 1/2 of the screen. In this way, the GPUs have extremely minimal information, allowing both GPUs to effectively behave as a single large/faster GPU with a correspondingly large pool of memory.

Ultimately the point is that gamers believe that two 4GB cards can’t possibly give you the 8GB of useful memory. That may have been true for the last 25 years of PC gaming, but thats not true with Mantle and its not true with the low overhead APIs that follow in Mantle’s footsteps."

To make things clear, this does not mean that Crossfire or SLI configurations on low level API's like DirectX 12 or Mantle will not make this happen by default, developers will need to optimise the game in order to take advantage of this technique. Traditional Multi-GPU techniques like alternate-frame-rendering will still remain the de-facto standard, at least in the near future.

We have already seen games take advantage of different Multi-GPU rendering techniques, for example Civilisation: Beyond Earth uses a technique called Split-Screen rendering which breaks a single frame into multiple parts, one per GPU, and processes the parts in parallel, gathering them into the final image at the end of the frame.

In the future low level API's may open a lot of options for us PC gamers, let's hope that we will all be able to enjoy the benefits of them sooner rather than later.

Join the discussion on the potential of Stacking of GPU Memory in Crossfire/SLI on the OC3D Forums.

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