[jallmann]

I think we're talking about different things? You seem to be referring to parallelism in the literal, general sense of the word, while I'm referring to computational parallelism. Basically, if Amdahl's Law doesn't apply, then you're looking at concurrency. So this statement

> from the perspective of the programmer, there's no difference between two threads running at the same time or by time sharing

is incorrect when you're talking about computational parallelism (as OP was), because you're not going to realize any speedups with time sharing. In that case, you're using threads as a concurrency mechanism -- not for parallelism.