In the Strange Land Of Robert Heinlein - 1984-09-05
Pulp writers were paid by the word, and if Heinlein writes fast now, he learned it when speed was of the pecuniary essence. L. Ron "Battlefield Earth" Hubbard, he says, was "the first writer I ever knew to have an electric typewriter. He was supposed to write at about 4,000 words an hour. I dunno about that -- but I've seen him write letters as fast as he could shove the paper in the roller. Actually, I think Isaac [Asimov] is a little faster."