4.3 Chapter Review
Congratulations, you can now write, compile, and run massively parallel code on a graphics processor! You should go brag to your friends. And if they are still under the misconception that GPU computing is exotic and difficult to master, they will be most impressed. The ease with which you accomplished it will be our secret. If they're people you trust with your secrets, suggest that they buy the book, too.
We have so far looked at how to instruct the CUDA runtime to execute multiple copies of our program in parallel on what we called blocks. We called the collection of blocks we launch on the GPU a grid. As the name might imply, a grid can be either a one- or two-dimensional collection of blocks. Each copy of the kernel can determine which block it is executing with the built-in variable blockIdx. Likewise, it can determine the size of the grid by using the built-in variable gridDim. Both of these built-in variables proved useful within our kernel to calculate the data index for which each block is responsible.