Bandwidth of dual channel DDR4-3600: 48 GB/s
Bandwidth of PCIe 4 x16: 26 GB/s
Bandiwdth of 3090 GDDR6X memory: 935.8 GB/s
Since neural network evaluation is usually bandwidth limited, it's possible that pushing the data through PCI-E from CPU to GPU is actually slower than doing the evaluation on CPU only for typical neural networks.
I once tried to start Firefox (back in the 2.5-3.0 days >:D) on a Celeron with 64MB RAM.
It worked perfectly fine, with the sole exception that the HDD LED was on solid the whole time, a single window took just over a literal half an hour to open, and loading a webpage took about 1-2 minutes.
https://www.microway.com/knowledge-center-articles/performan...
https://en.wikipedia.org/wiki/List_of_Nvidia_graphics_proces...