I tried to find gc problems in 21.2 xemacs, but all I could find was already known: - cons cells take 50% more storage in 21.2. - pure space is gone, so gc will always take longer by a fixed amount. If your physical memory size is near the size that will cause thrashing, the 50% extra space _could_ translate into 10 times more clock time used. For me, 21.1 is faster at gc only by less than 25% when I run (progn (compile-and-profile (let ((count 9000000)) (while (> count 0) (setq z (cons 1 2)) (setq count (- count 1))))) (compile-and-profile (loop repeat 10 do (garbage-collect)))) So, to fix this we need to: - make cons cells take up only 2 words using the Big Bag of Pages technique (perhaps too hard?) - implement some kind of generational gc. We've paid a pretty high price so far for portable dumping. Let's try to minimize it. Martin