[mikeash]

#1 sounds like a pretty minority viewpoint. OSes these days are a lot more than just the kernel and things that call into the kernel. If you do a fresh install of the OS then I think what you find on the disk afterwards can all be reasonably referred to as "the OS."

#2 does not apply here. This particular API isn't implemented inline, or with compiler intrinsics, or assembly. They're actual calls.

If you're talking about the general concept of atomics, then I agree that "OS atomics" is a dumb name. But we're not talking about that. We're talking about a specific API that happens to implement that general concept. That specific API is part of the OS.