Well, "working vs waiting" is the same as "CPU vs I/O", so we're saying the same thing here. As to your "concurrency vs parallelism" distinction - it's one val

Well, "working vs waiting" is the same as "CPU vs I/O", so we're saying the same thing here. As to your "concurrency vs parallelism" distinction - it's one valid one, and pretty widespread; I think it misses a lot of important points though, and I wrote about it here: http://www.yosefk.com/blog/parallelism-and-concurrency-need-different-tools.html http://www.yosefk.com/blog/parallelism-and-concurrency-need-... One point from there is, a parallel mergesort is conflict-free while say a concurrent DB-backed web app has a lot of opportunities for conflicts (2 users want to take the same username - who wins? etc. etc.) I argue that the many differences between such systems result in rather different tools being suitable to build them.