The Host–Device Model
Before any of the CUDA syntax in the next section makes sense, one structural fact has to be settled: a discrete GPU is a separate computer. It has its own memory, its own processors, and no automatic view of what the CPU is doing — every byte the GPU touches had to arrive there deliberately, and every result has to leave the same way. This page names that structure once, independent of any specific API, so that the CUDA-specific mechanics in Your First Kernel land on a model you already have rather than a pile of new syntax to memorize.