Focus on the Radeon R9 390X 8GB
The only card among those we tested that demonstrated better results under DX12 was the Radeon R9 390X, and as we surmised on the previous page, this may have to do with a combination of CPU use, VRAM, and system RAM. We decided to add another set of benchmarks after we initially published this piece, as readers were curious about the 390X results.
As you'll see below, they were no fluke.
And what about the CPU and RAM usage? Well, here you have the results under DX11:
And here they are under DX12:
Note that RAM use shoots way up when moving to DX12, from 4.6GB to 6.9GB in this example, while CPU usage flattens out, avoiding peaks on any particular core. We think these two factors are what allow the R9 390X to perform with a higher minimum, and given that it was the only card we saw that demonstrated this repeatedly, we conclude that it must have to do with VRAM, as that's the only significant difference between the 390X and all of the other cards we tested.
And this isn't just wild conjecture; the game's developers have actually included a warning right in the options menu indicating that "Very High" settings can require more than 4GB of VRAM. We're pretty sure we're finally seeing this demonstrated in our benchmarks, but for whatever reason, it took DX12 to really bring out the benefits of more VRAM. And apparently the GTX 980 Ti 6GB isn't benefitting in the same way.
In case you haven't realized it yet, this is just a first look at DX12 performance on the PC. Much remains to be analyzed, with more in-game benchmarks on a wider variety of systems. But if our results are any indication, this will not end up being an technology that favors one brand of GPUs or the other. It's really all about the CPU, and whether DX12 ultimately helps or hurts performance on a given video card really isn't the issue; it's what DX12 allows developers to do that they could not do before. We won't see the true benefits of this until DX12-only titles are released, which likely is still a ways out. For now, based on our results in Rise of the Tomb Raider, we'd say users of both Nvidia and AMD cards can rest assured that they aren't going to be penalized as DX12 rolls out. Interestingly, however, we may have finally found a game that truly benefits from more than 4GB of VRAM, and for whatever reason, it only does so under DX12. The plot thickens!
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