Windows 10 will be coming with DirectX 12. DirectX 12 is the first version of DirectX that really uses multiple cores effectively.
Below are two slides provided by Microsoft:

DirectX 11: See how much of the work is done on the first core?

DirectX 12, the work gets split up.
Bottom line: In DirectX 11 this frame took almost 9ms to render. In DirectX 12, it took about 4ms. Now, how much real world improvement you get depends heavily on both the developer and the game. But the reason we’re all getting so excited is that DirectX 12 should be the biggest performance bump for those who utilize it we’ve ever seen.
What this means to you
Next time you watch Jurassic Park or Phantom Menace, please realize that the CGI in those movies can be done in real-time today. However, most graphics engines in games still render scenes very differently than in movies. That’s because it’s only recently been possible to create real-world fidelity in real-time. But a modern machine with DirectX 12 (or Mantle) could do real-time visuals in a game that is as good as you would get in say Lord of the Rings.
The Post-Frame Rate game world
We will need get away from frame rate as being the key metric on its own (unless we’re comparing apples and apples). The DirectX 12 / Mantle specific games will look unmistakably different than what we have today.
What we basically do today in games is render a frame and then apply a bunch of post-process effects to it. In a DirectX 12 / Mantle world we’ll render images the same way they did CGI in the past. With a modern CPU + GPU combo with DirectX 12 you could do parts of the Battle of Helms Deep from LOTR in real-time. Keep a very close eye on Unreal 4, Frostbite, Crytek and of course Nitrous.