understanding 9grid and clustering (part 2) ?

maybe i can add that i have some experience with linux clusters, beowulf 
and mosix type.
on beowulf cluster programmer has to use special libraries (MPI or PVM) 
to write parallel programs.
on mosix cluster every kernel has patch enabling processes to jump from 
home node
to other nodes within cluster, so if programmer wants paraller program 
running
on different nodes he can use fork().

how can be 9grid compared to this two types of linux cluster?

thanx again for answers.
alexandr babic.