title: How does event driven I/O allow multiprocessing?
body: <p>I am aware of event driven I/O like select, poll, epoll, etc allow someone to build say a highly scalable web server, but I am confused by the details. If there is only one thread of execution and one process running for the server, then when the server is running its "processing" routine for the ready clients, isn't this done in a serial fashion to process the list of ready clients since it can't be scheduled on multiple cores or cpus? Moreover, when this processing is happening...wouldn't the server be unresponsive? </p>
  
  <p>I used to think this was the reason people used thread pools to handle the event I/O on the backend, but I was confused when I heard recently that not everybody uses thread pools for their applications. </p>