DirectX 12 Update Allows CPU and GPU to Access VRAM Simultaneously

Not to nitpick, but the bus doesn’t change size. What’s changed is the size of the window representing how much VRAM the CPU can see at once. If the CPU needs to send 1GB of data to VRAM, it can normally only send 1/4 of that, then it has to move the window, move the next 256MB, and so on. It’s analogous to EMS back in the day. Rebar makes the window bigger.

The Microsoft blog post Tom’s references says “With the VRAM being managed by Windows, D3D now exposes the heap memory access directly to the CPU! This allows both the CPU and GPU to directly access the memory simultaneously, removing the need to copy data from the CPU to the GPU increasing performance in certain scenarios.”

To me this new feature sounds more like the equivalent of giving the CPU DMA to the VRAM without an intervening buffer.