And to demonstrate that hard realtime is not about speed, there is a whole hard-real time JVM implementation with GC and everything used in military contexts.

And to demonstrate that hard realtime is not about speed, there is a whole hard-real time JVM implementation with GC and everything used in military contexts. Modern computers are ridiculously fast, relatively speaking you don’t need much resources to calculate a missile trajectory, so “simply” 100% sure doing some calculations at a fixed rate, with even a GC cycle that has a deterministic higher bound (e.g. it will go throw the whole, non-resizable heap, but it will surely always take n seconds), you can pass the requirements. Though a desktop computer pretty much already begets the hard part of hard realtime, due to all the stuff that makes it fast - memory caching, CPU pipelining, branch prediction, normal OSs scheduling, etc.