RT GPU: What is needed to use system RAM

[Morne]

So I was listening with half an ear to ChaosGroup Lab's latest podcast about RT GPU and was wondering, is there anything stopping Chaos from using the system RAM for the GPU? Is it a hardware limitation or is the current limitation in the API between the graphics vender and the graphics driver?

Is Nvidia's project Pascal suppose to bridge this gap or are we still FAR off from using system RAM?

[Macker]

I think AMD HSA was supposed to address this?

[joconnell]

Is part of the problem the slowness of the bridge between the gpu and system memory though, as in it'd kill the benefit of gpu speed?