Question about how GUM works

Hi All, I have a question about GUM - the runtime system for Parallel Haskell. There are below words in the paper addressing GUM architecture: "The first action of GUM program is to create a PVM manager task, whose job is to control startup and termination. The manager spawns the required number of logical PEs as PVM tasks, which PVM maps to the available processors." So my question is how many PEs the PVM mamager task will spawn? The number is accordant with the processor number or determined by some other things? And will the number of PEs be changed during the execution of the program or not? Thanks, Qing Yang qing.yang@intel.com