Hi, This could be a bit off the list, but still ... The output of uname -a of my machine is as below Linux achala 2.6.11.4-21.8-smp #1 SMP Tue Jul 19 12:42:37 UTC 2005 i686 i686 i386 GNU/Linux, and I guess SMP stands for Shared Memory Processor. I have a two processors on my mother board. I am doing my work in Molecular Dynamics simulations. So most of the time I would be doing a lot of number crunching. Now if start a job on my machine, does it automatically run using both the processors on my machine, or will I have to use a message passing library like MPI to use both the processors? I experimented with this some time back, I ran the same job with ./executable and also mpirun -n 2 ./executable on my machine (no clustering or anything). The second one gave maginally better results and top showed two processes running. Can someone explain what's happening? Regards, Chaitanya. __________________________________ Yahoo! Mail - PC Magazine Editors' Choice 2005 http://mail.yahoo.com