Why does PLINQ use only two threads?

Question

Say I have an IO-bound task. I\'m using WithDegreeOfParallelism = 10 and WithExecution = ForceParallelism mode, but still the query only uses two threads. Why?

I und

Answer 1

10 is maximum

Sets the degree of parallelism to use in a query. Degree of parallelism is the maximum number of concurrently executing tasks that will be used to process the query.

From here:

MSDN