It's funny, a long time ago, my brother and I were debating what would be a good definition that draws a line between a real "computer", as opposed to a calculator/controller/toy/etc. I was advocating running a real OS kernel as a heuristic (but then you'd have to define what a "real kernel" would be), and him, being a Doom fan, came up with:
"It counts as a real computer if it runs Doom."