I'm not sure what you mean by "system" here, but if the OS does it then the architecture is probably not cooperative, but rather preemptive. On the other hand,

I'm not sure what you mean by "system" here, but if the OS does it then the architecture is probably not cooperative, but rather preemptive. On the other hand, if the runtime (such as the Go runtime) causes a context switch between coroutines because one of the coroutines is waiting (on blocking I/O, etc.), then the architecture could still be considered cooperative because the scheduling is such that none of the coroutines would ever be actually preempted by the runtime while executing instructions. Of course, they could still be pre-empted by the OS because they're ultimately all running as system threads, which is one of the downsides of all this: eventually, it all comes back to threads, how many of them are present, and how the OS handles them.