Difference bewteen Direct3D 11 and 12?

[Shichiya San]

I've been playing Super Paper Mario for the past few weeks with Direct3D 11 and had a lot of FPS drop at certain point (or rather 30fps lock).However once I changed my graphic option from Direct3D 11 to 12,the game runs 60fps smooth at most scenario. So whats different about these two?

My specs: GTX1060 6GB ,I5 750@2.67Ghz 4 core and 12GB ram