alt Hacker NewsOften you don't move memory around as a programmer, but that's exactly what happens in the background.
It's the address space that's unified, not always the physical hardware.
The data movement (when needed) is handled transparently in the background by page faults and other tricks.
Moving memory around is a bottleneck. Non-unified memory usually means copying over the PCIe bus which is way slower than RAM (and way way slower than VRAM). Actually unified memory means you don't need to copy anything at all though which is the absolute best case for performance.