One Dev Question with Raymond Chen - What Programming Language is Windows Written In?

The 'One Dev Question with Raymond Chen' video series is part of the One Dev Minute channel.  In this series, longtime Microsoft developer and semi-official Windows historian Raymond Chen covers a series of questions about Microsoft Windows development, team culture, and/or history.  If you have additional questions for Raymond, please add your questions in the comments section below.  You can also find out more development details about Windows and its history on Raymond's blog.