The short answer is "backwards compatibility". The long answer is... well, it's the rest of this video. MORE BASICS: https://www.youtube.com/playlist?list=PL96C35uN7xGLLeET0dOWaKHkAlPsrkcha Written with Sean Elliott https://twitter.com/SeanMElliott/ Graphics by William Marler https://wmad.co.uk Audio mix by Graham Haerther https://haerther.net/ I'm at https://tomscott.com on Twitter at https://twitter.com/tomscott on Facebook at https://facebook.com/tomscott and on Instagram as tomscottgo