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.
Memory-Bound vs Compute-Bound
Knowing a kernel's arithmetic intensity puts it on the roofline plot in theory; knowing whether it is actually memory-bound or compute-bound in practice requires measuring the running kernel, because achieved bandwidth and achieved compute throughput are never the datasheet peaks the paper estimate assumed. This page turns the roofline classification from Arithmetic Intensity and the Roofline Model into a concrete diagnostic you run against a profiler, and adds the case the roofline model doesn't represent at all.