there's windows, there's the mac os, there's linix, and there's a lot of others that are smaller in their purposes. >> host: well, craig timberg, as you mentioned, your fourth piece in this series was on linus to o have volt? >> guest: so he's this amazingly bright guy who, as a college student in helsinki, finland, created an operating system not quite from scratch. he built off the work of some other people. but the thing that he did that was really revolutionary is he made it available to anyone who wanted it. it's a developed model called open source. so he did, you know, the first, i don't know, hundred things you needed to do right to make an operating system work, and then he basically said to the world, okay world, send me your improvements and your updates to this thing, and the world did to the point where hundreds of thousands of computer developers eventually were involved in creating this operating system. so he releases it to the public in 1991. there's about 10,000 lines of code. here we are, it's 2015, so 24 years later, and now there's 19 million lines of code. he didn't