Comment by wizofaus

"a program which is not written as concurrent can never be executed as parallel"

Unless of course you're running multiple independent instances of it, each with different parameters, which I gather is a pretty common way of running long running CPU- intensive operations on large data sets. Presumably there's often some final separate step that may be needed to combine the results once they're all finished, which if run manually obviates any concurrency concerns at the software level.