To be fair, MS did not revolutionize computing when it was founded. They didn't make anything that everyone else wasn't already making. I'm trying to think of a single thing that they did before the company was worth a billion dollars that was in any way revolutionary, technically. I can't think of a single thing (lots of stuff since then, BTW, but I think that's a bit unfair ;-) ). They executed well, both in development and in business and they had a good combination of good business foresight and lucky breaks. They were also pretty ruthless.