Thanks for the link. I did the tests on an SGI SMP machine that, if I understand correctly, shares the memory much better than most other systems. I will read about these different components and see what I can figure out.

Thanks,

Francis

You need to understand the issues of memory bandwidth shared between cores and between processors, memory affinity and thread affinity ("binding") see http://www.mcs.anl.gov/petsc/documentation/faq.html#computers

Barry