[sasa555]

I like to think of it as preemptive because (putting NIFs aside) it's not possible for a single process to completely block the entire scheduler, even if it ends up in an infinite CPU bound loop.

So in other words, a task (i.e. process) doesn't have to cooperate with others. It can do whatever it wants, be it I/O or CPU bound, and doesn't have to yield explicitly. Due to aggressive "preemption" it won't block other pending tasks significantly.

In contrast, if this is not guaranteed (which is not in most other Erlang "alternatives" I've looked at), then a task might accidentally paralyse large portion of the system.