Indeed, there is a pool of OS threads, a pool of Haskell lightweight threads, and a spark pool. Check out these papers: * Runtime Support for Multicore Haskel

Indeed, there is a pool of OS threads, a pool of Haskell lightweight threads, and a spark pool. Check out these papers: * Runtime Support for Multicore Haskell[1] * Seq no more: Better Strategies for Parallel Haskell[2] [1]: http://community.haskell.org/~simonmar/papers/multicore-ghc.pdf http://community.haskell.org/~simonmar/papers/multicore-ghc.... [2]: http://community.haskell.org/~simonmar/papers/strategies.pdf http://community.haskell.org/~simonmar/papers/strategies.pdf