[Hadoop-common-user] multiple threads

Does Hadoop run multiple threads on a single slave? In my current
experiment, I'm running with three slaves, each of which has four
processors. Hadoop only appears to be using one processor on each
slave. It's very possible that I've made a configuration mistake.

I have mapred.map.tasks set to 7 (this should be enough to see two jobs
on each client, though I plan on eventually setting it higher).
mapred.tasktracker.tasks.maximum is 3 (eventually this will be higher,
too).

Thanks.