What happens when a GPU reads memory

This is a type of article that is HN worthy and came to HN for initially because I don't even understand a third of content there. Giving me inspiration to dive deeper.

SEriously, I don't understand it (yet) lol.

VERY good article, reminds me on:

"what every programmer should know about memory" https://github.com/Ty-Chen/Reading-List/blob/master/What%20e...

For a long time, the chip manufacturers had an inclination to simplify the hardware and rely on the software adapting and optimizing. But for decades this bid failed. Now we have the unrelenting AI capable of finetuning kernels relatively quickly. Maybe simpler hw will work this time? Note: not sure if TPU/NPU is not only simple but also too limited.

Can someone help me understand why I spent 5 minutes reading something that I still don't understand?

Link for the ELI5 version?

YMMV; not all GPUs work exactly like this

Ctrl+F PCIe BAR.. nothing.