The copy happens much faster because for unified memory, the data is actually only moved when actually needed on one device. So if you just say, this is not on gpu. It makes a GPU Tensor that references a CPU Tensor (no copy happens here). Now if you access some values of that GPU Tensor in a kernel, then the data will be copied from the CPU to the GPU for the operation to be performed.
You couldn’t get 110x in transfer, the PCIe connection is the limit, and our current transfer speed is pretty close to it (not sure exactly how close).