Don't forget also that when your CPU shares time, it divides up the time equally among the processes. So if your application creates 20 processes, it takes a disproportionate amount of CPU time (I believe, someone correct me if I'm wrong).
It depends on the OS. In most cases, threads are the only schedulable entity (think of a classic process as containing one thread), so there is no difference between 20 single-threaded processes and one process with 20 threads.
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Don't forget also that when your CPU shares time, it divides up the time equally among the processes. So if your application creates 20 processes, it takes a disproportionate amount of CPU time (I believe, someone correct me if I'm wrong).
It depends on the OS. In most cases, threads are the only schedulable entity (think of a classic process as containing one thread), so there is no difference between 20 single-threaded processes and one process with 20 threads.