de Carabas wrote:Presumably this only applies if the game is written to take advantage of it?
Yes and no.
Win10 will know how to take better advantage of hardware that's in your PC. Also - if you have SLI / Crossfire running, windows will treat it as a single device - NOT two as it worked so far. This gives you better overall performance unlike current states where your max benefit would be an extra 40% boost.
When it comes to DX12 - it's a very different API compare to previous DX versions. It doesn't just give developers new shiny effects to play with, it also treats our GPUs differently and in conjunction with Win10 - uses them much much better so you won't have poor framerate while your GPU sits at 40-50% load.
It is said that even old GPUs up to GTX4xx series will suuport DX12. Not all effects and features though but it will work.
Basically - it's the new DX engine + new Windows that utilize hardware much better than any previous combination.