Usage of "shut down" is more prevalent and has a longer history in English, although "shutdown" is also correct and has entered wide usage at the beginning of 2

Usage of "shut down" is more prevalent and has a longer history in English, although "shutdown" is also correct and has entered wide usage at the beginning of 20th century. Google NGram Viewer ftw: http://books.google.com/ngrams/graph?content=shutdown%2C+shut+down&year_start=1800&year_end=2000&corpus=0&smoothing=3 http://books.google.com/ngrams/graph?content=shutdown%2C+shu... (Notice the cool bump for "shut down" around 1940s: apparently lots of things were being, ahem, shut down.)