The exact terminology probably depends on your programming environment as well. I'm using Node.js now and async IO (e.g. for disk access) uses a threadpool behi

The exact terminology probably depends on your programming environment as well. I'm using Node.js now and async IO (e.g. for disk access) uses a threadpool behind the scenes but these threads use very little CPU: they're mostly idle in fact; their only two responsibilities are to start the IO operation then send back the data to the parent process when the IO completes so these threads use almost no CPU so they're not a problem but I guess it depends on how heavily they are used. Node.js is not really designed to be a DB engine though so this design works well.