According to <sjenkin(a)canb.auug.org.au>:
Developers of Initial Unix arguably were 10x-100x more
productive than IBM OS/360, a ‘best practice’ development at the time,
so what CSRC did differently is worth close examination.
Ken Thompson was an astonishingly productive programmer. I don't think
you can build a business plan that starts with "hire someone like
Ken."
One weekend just for fun he pounded out most of an APL interpreter,
which I then took and spent a month part time adding a few features
like saving and loading workspaces, and adjusting it to use the APL
character set on our funky bitmap terminals at Yale. He did more in
the weekend than I did in the month, and I am not a terrible
programmer.