How to keep background processes from slowing down my program

[Matthew A Machlis]

I am working on a realtime graphics simulation for which it is critical that
every loop through the program take the same amount of time to run.  I
realize that the drawing routines will take variable amounts of time to
execute depending on what exactly is being drawn on the screen, and can
account for this by forcing the program to pause a bit if the loop runs
faster than usual.  However, in timing the program I have noticed that 
occasionally a loop will take much longer (up to 2-3 times as long) as the
average loop time.  All I can think of is that some background process is
interrupting my program to do something and taking up this extra time.  Is
there any way I can stop this from happening?  I can use "nice," but only
the super-user can execute programs with higher priority than usual, and
running my program as the super-user all the time is not an option.  Is 
there any way to boot up the machine such that it doesn't run all of the
background filekeeping tasks?

I would appreciate any info anybody might have.

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Matt Machlis
MIT Space Systems Laboratory
(617)253-2272