Added OpenMP - MPI comparison slide

lectures/hardware/slides.qmd

@@ -116,6 +116,21 @@ If we want to scale beyond one node, what do we need in our example?
   * Often used for boundary exchange
 * A lot of the details are beyond the scope of this lecture.
 
+## OpenMP vs MPI
+
+:::{.smaller}
+
+| OpenMP | MPI |
+| ------ | --- |
+| shared memory | distributed memory |
+| can't scale beyond one node | can scale across many nodes |
+| uses independent threads| uses ranks that need to communicate with each other |
+| pragmas inserted in the code tell the compiler where to parallelise | API to vendor specific libraries |
+
+* OpenMPI is a MPI implementation and has nothing to do with OpenMP 
+
+:::
+
 ## Collectives 
 * Collective communication that involves a group of processes (ranks)
 * Examples: broadcast, gather, scatter, reduction ...