Generally, patents cover a physical process or product, and copyrights protect ideas and written works. The reason there are not that many software patents probably has to do with the idea that software is generally considered to be intellectual in nature rather than physical and a patent won't protect your rights to something as long as a copyright will. You get one copyright on your idea, you're done. It's protected until you've been dead about 25 years. I can't remember exactly how long the term is on a patent, but I do know that if you miss a window to renew it, it becomes public domain. Even if you do renew a patent, it can only be renewed so many times before it's considered public domain.
That's what my previous research into the whole thing yielded for me, anyway.
That's what my previous research into the whole thing yielded for me, anyway.