Hello This is NOT another "Is GPU X bottleneck by CPU Y ?" type of topic. I know my CPU does (trust me on this), and please don't even try to say to me "CPU bottlenecks don't exist", My question is simple : Can CPU performance decrease GFLOPs generated by the GPU ? I mean, GPU driver must do something on CPU for GPU to do anything (right ?). So, is there a point, at which CPU isn't fast enough to get from GPU it's full processing speed, because driver execution is so slow ? Short history lesson (for those that don't remember how old stuff works) : Before BCLK, there was this thing FSB bus. It was good bus at the begining, but after a while it's flaw was clear : By design, it was responsible for ALL transfers from and to CPU. Be it from RAM, HDD or PCI-e/AGP devices - all data that went to CPU had to go through it. At one point, FSB wasn't getting fast enough to cope with data from new CPUs and other hardware. To check if this is possible, I did something no human has ever done : I put GTX 1080 FE in PGA 478 MB with Celeron 2.0A (Northwood-128 core) in it, and downclocked that to 1,9GHz (for good measure) Result in AIDA64 : ^I added PCI-e bandwidth table to show how slow both RAM and PCI-e sub systems are at this point. CPU-z valid : https://valid.x86.fr/2sve04 To better showcase what I done : Because I decresed FSB frequency to 380MHz (effective) and 95MHz (real), bandwidth available to everything was reduced to 3080MB/s (theoretical). That's NOT enough to saturate a PCI-e 1.x x16 slot, let alone DDR2 memory or anything hard disk related. Now, on GPGPU benchmark from there clearly is a slowdown. However it's in GPU Copy (which should have 250 000 MB/s+), and not so much on 32-bit Single Precision test. Can someone explain to me why single precision FLOPs didn't went down so much (20% from theoretical), when driver clearly is limited by CPU processing speed (over 20% drop on internal memory copy speed) ? Thank you.