Not at all my experience with MIT Lisp Machines, and I can't imagine the Symbolics ones were that sort of unusably worse, unless configured to be so, or you wer

Not at all my experience with MIT Lisp Machines, and I can't imagine the Symbolics ones were that sort of unusably worse, unless configured to be so, or you were using the very first releases of the 3600, which were late and at least to some degree rushed to market. State of the art in the early '80s on the original CADR hardware and software was 2 space incremental but not generational copying GC. Every cons (memory allocation) would invoke the copying GC to do a bit of work, and once done the flip was transparent. Generational GC, which I didn't experience, was a big thing because the above had lousy locality and frequently/generally? cause page faults, making the pauses noticeable and obnoxious, but not the end of the world (perhaps most wouldn't even notice if not watching the three bars at the bottom for computing, paging and GC).