Device Memory and Bandwidth
Every figure in Arithmetic Intensity and the Roofline Model ultimately rests on one number: how many bytes per second a kernel can move between the SMs and DRAM. That number is set by the physical memory technology soldered onto (or stacked next to) the GPU die, and it is very different from the number a datasheet advertises. This page covers what GDDR and HBM actually are, why achieved bandwidth always falls short of the peak figure, and how to measure the one that actually matters for a given kernel.