first beofwul

Mat Harris mat.harris at
Thu Jan 2 14:21:40 PST 2003

On Thu, Jan 02, 2003 at 05:07:47 -0500, Mark Hahn wrote:
> > Please can someone explain what MPI and PBS do.
> MPI is a programming interface that makes it easier to write
> a program that runs concurrently on multiple processors and/or hosts.
> it's a message-passing interface, which means that the program 
> tells it things like "get element 43 from the array called 'foo'
> from the 4th process".  or "send this value to all other processes".
> > I understand PBS to be
> > something where I give it a normal, non-cluster-optimised program and it
> > will distribute the workload over a listed set of machines.
> I'm not sure what you mean by "non-cluster-optimized".  either a 
> program is designed to operate on multiple processors or machines at once,
> or it isn't.  there's no separate "optimization" step.

by "non-cluster-optimized" i meant that it will run one thread on the local
machine and is not in any way aware of the cluster. I will work on one
system (possibly on more cpu's if it is an smp system).

> PBS is a batch/queueing system.  it can indeed run non-parallel
> applications, but can also run parallel ones.  fundamentally,
> the operation is the same: find a set of idle (or low-load) machines,
> and find something for them to do.  a non-parallel job obviously 
> needs only one process.

what i was meaning is if I have a program to work out the value of pi to 500
places, it will take a while so could you do something like, and I know i'm
being naive here:

./pbs-program /home/matthewh/pi-calculator /root/hosts_to_run_on

whold a pbs program do anything like this

I know I am probably barking up the wrong forest and I expect to get told
"No, you have to wrok out how to code C", correct?

Mat Harris			OpenGPG Public Key ID: C37D57D9
mat.harris at	
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