Apropos: http://www.nytimes.com/2014/04/01/business/supreme-court-seems-wary-of-a-software-patent-case.html

There are two ways software can be novel: it can be a new way to do something, whose embodiment is a software program, and it can be a new way to get a computer to do something (which itself isn’t necessarily novel).

In the first case, the computer might be a practical necessity, but the process must be novel even if it were performed by an army of accountants. In the second, the process could be mundane, but involved elements which no expert before knew (or could easily have known if they set their mind to it). In the latter case, the process itself is not properly patented, but the elements that make it novel.