My first development job was as a software developer at Bell Labs in Naperville working on the 5E. I started at the end of 5E4 (the 4th revision) and then worked on 5E5 and 5E6. I went from school writing maybe 1000 line programs to maintaining and enhancing a system comprised of millions of lines of code and hundreds of developers. Most of the code itself was very simple but it was the interactions between modules and switching features that was very complex.