I remember, at Xerox, operating systems written in Smalltalk-76 and Interlisp. Great user interfaces for the day and when something broke the debugger was helpful - or you could just blow away the debug window and continue. The Smalltalk-76 footprint was a megabyte or so and the interlisp footprint was about 10 megabytes. This was with editors and printing etc.
Of course the big board computer with 64 kilobytes of RAM and 2 8" floppies booted in less than a second.