I guess anything is an implementation detail depending on what level we're talking about, but each layer is constrained by the "previous" layer in some ways, an

I guess anything is an implementation detail depending on what level we're talking about, but each layer is constrained by the "previous" layer in some ways, and we're working within those constraints. Sometimes we have the luxury of not caring about this, and we can let the language runtime pick what it wants to do, and abstract it away for us. But sometimes you need to care, because you're constrained by the existing environment/conditions the code runs in, and need specific control over eg like timings. I think in an ideal world where we can start from scratch and aren't constrained by existing tech stacks/layers/hardware, maybe the OS and compilers (and runtimes) could integrate more tightly when it comes to threading, stack, and memory management. It would be a radically different architecture, though (and I dunno which layers we'd need to invalidate).