I worked on the Windows kernel in the early 2000s. I really enjoyed it - I learned a lot about PC hardware, worked with some very smart people, and although a few projects were ambitious and ambiguous and didn’t really pan out, most of them were really solid; it felt great to be improving something that really made a difference for a huge number of people. I’m a much better developer, with a much better sense for how code serves business, for having spent time there.