Today we are hearing that the low-level Vulkan API will not support multiple GPUs on Windows 7 or Windows 8.1. The Dark Side Of Gaming came across the disappointing bit of news when rummaging through Khronos Group’s slides from GDC 2017. One slide entitled “Vulkan Multi-GPU and Virtual Reality Support” clearly points out that “WDDM must be in ‘linked display adapter’ mode”, with WDDM referring to the Windows Display Driver Model.
Although it might not seem like a big deal from reading that line, the linked display adapter mode is exclusive to WDDM 2.0. And as you are probably coming to realize at this point, WDDM 2.0 is a feature that is only natively supported by Windows 10. In other words, if you want to use NVIDIA SLI or AMD CrossFire natively with Vulkan, you’re going to have to be running Windows 10.
However, even upgrading to Windows 10 won’t guarantee you multi-GPU gaming bliss. Just like with DirectX12, multi-GPU support must be manually added into titles with Vulkan. So, you’re still going to have to rely on developers to actually add support in the first place.
Here’s one more wrinkle in this story; it appears that Linux won’t have the multi-GPU limitation when it comes to Vulkan (and it obviously doesn’t support WDDM) which makes us wonder why exactly Windows 7 and Windows 8.1 are being shown the door...