Erlang's VM runs a scheduler on top of a number of OS threads. If an actor blocks, that actor won't be scheduled to run until the blocking call is finished, but

Erlang's VM runs a scheduler on top of a number of OS threads. If an actor blocks, that actor won't be scheduled to run until the blocking call is finished, but you won't consume a whole OS threads, and other actors will be able to run while waiting for completion.