I work in medical robotics and I can tell you that a lot of our code is quite old, and we have a culture that code you write will stay around. Some things don't

I work in medical robotics and I can tell you that a lot of our code is quite old, and we have a culture that code you write will stay around. Some things don't change for example optimal control algorithms, while others things are very difficult to change such as network routing. So, while the applications get re-written on the 4-10 year time frame parts of the OS are 15+ years old.