Please don't make us guess. UNIX is not a brand name. Is this HP UNIX?
here is how to use a RAM drive in HP UNIX, though they call it "unsupported and dangerous"...
Since it has four processors, you could try running four simultaneous jobs. That way, one job would only need to complete in 1200ms to get the required throughput.
If you have enough buffer cache, RAM disk versus normal disk shouldn't matter a huge amount. All changes get cached in RAM anyway.