@screwlisp on the Xerox 1108 (Interlisp-D) on which I was first able to compute (recursively) bignum factorials, factorial 1000 took just over twenty minutes. I therefore didn't even think of trying to compute anything larger. It's been my standard benchmark of Lisp stack performance ever since!
My Acorn A440, in 1987, could do it in 4 seconds (Cambridge Lisp); a TI Explorer I tested in 1989 could do it in 0.3 seconds; these days, my laptop can do it in 0.000064 seconds of wall clock time.
@screwlisp there's a lot to like about the Interlisp spaghetti stack — it seems to me the most natural native multi-tasking implementation in Lisp I've seen, at least until #Clojure — but it was not fast!
