title: What happens when VRAM is full?
body: <p>I want to know the current nvidia/AMD implementation of handling VRAM resource allocation.</p>
  
  <p>We already know that operating systems use swap/virtual memory when system RAM is full, then what is the equivalent of swap when it comes to VRAM? Do they fall back to system RAM or hard disk?</p>
  
  <p>I thought that falling back to system RAM is rational, but from my experience video games lag horribly(1/20 of typical FPS) when they are out of video memory space, that made me doubt that they are using system RAM because I think system RAM is not that slow to make the game lag so much.</p>
  
  <p>In short I would like to know what the current implementations are and what is the biggest bottleneck that causes the game to lag under out-of-memory situations.</p>