The choice of a Dell Optiplex business desktop PC for a month-long calculation in 2008 is interesting for historical reasons.
A decade before that, Sun workstations that cost $30k each were used for long-running engineering tests like chip verification, while an Optiplex is less than 10% of that.
Well, in 1998, I was running a dual-processor Dell Optiplex at 400MHz for month-long simulations; it cost $5000 at the time. but yeah, most people around me were buying $25k SGIs that had about half the oomph of my machine. I think that was the year it became clear Intel was going to get enough floating point and cache to be competitive with the RISC UNIX systems.
A decade before that, Sun workstations that cost $30k each were used for long-running engineering tests like chip verification, while an Optiplex is less than 10% of that.