Not sure if this is the correct section but I just found this and thought it would be interesting to share it. It talks about the language in which Windows is written but I was shocked by the code size.
QuoteThe full source tree with all the code, test code and everything that together constitutes the “Windows source code†is more than a half terabyte in size, in more than 1.5 million files. You can spend a year (seriously) just drilling down the source tree, a couple of hundreds of thousands of folders containing the code for every component making up the OS workstation and server products and all their editions, and see what’s in there, read the file names and try to figure out what does what. It would take a life (or two) to read it all.
https://www.quora.com/Which-programming-language-is-used-for-making-Windows-10