DIRECTX 12 AND 12_1: WHAT’S THE DIFFERENCE?
by Windows 10 is rolling out for free to PCs across the globe, and it's at the center of many things, not least Microsoft's universal app strategy to grow the selection of Windows Phone apps by getting developers to create apps for Windows 10 desktops.
But there's one other reason why Windows 10 matters, and that's DirectX 12. Touted as a next-generation application programming interface (API) that offers lower overheads and more efficient utilization of multi-core CPUs, DirectX 12 promises improved performance for gamers all over.
That sounds great, which is why DirectX 12 has been the center of a lot of hype and also a lot of confusion. Considerable discussion has arisen around DirectX feature levels and version numbers, and you may have seen DirectX referenced variously as DirectX 11.1 and 12_1. As it turns out, that's not due to varying house styles and the two are in fact quite different things.
A DirectX version update adds a new set of standardized capabilities that give developers more tools to do their jobs better. In the case
NOVEMBER 2015 of DirectX 12, that would be the ability to have lower API overheads, improved utilization of multi-core CPUs, and the ability to combine the graphics processing capabilities of non-identical GPUs.
On the other hand, a DirectX feature level is a clearly defined set of GPU functionality. It defines the minimum level of support a particular GPU needs to offer while still supporting the underlying DirectX specification. Note that we said minimum levels of support, so even though feature level 12_1 specifies support for conservative rasterization Tier 1, a card like NVIDIA's GeForce GTX TITAN X actually supports Tier 2.
Ultimately, despite their similarities in naming, feature levels aren't really related to the DirectX 12 API, which is why a card that supports only feature level 11_1 can still support DirectX 12.
Take the AMD Radeon R7 370 for example. Even though the card supports only feature level 11_1, it can still take advantage of the key benefits of DirectX 12 like more direct access to GPU hardware for the API. However, it will not benefit from aspects of feature level 12_1 like volume tiled resources and conservative raster.
DirectX feature levels are pre-defined sets of GPU functionality.