The boring answer is that standard atomics didn't exist until C++11, so any compiler older than that didn't support them. I think most platforms (certainly the popular desktop/server platforms) had ways to accomplish the same thing, but that was up to the vendor, and it might not've been well documented or stable. Infamously, `volatile` used to be (ab)used for this a lot before we had proper standards. (I think it still has some atomic-ish properties in MSVC?)