Since installing the latest security patch, Safari has been painfully slow. Can anybody suggest why? Other than that, I thought it might be useful to collate a list of reasons, however trivial, that your computer might be running slowly, along with ways to fix it. Hopefully one will work for me. I'll start the ball rolling: Check how much space is left on your computer. It is recommended that you keep at least 10% of your HD free for optimum performance and to avoid major system crashes. Also, Safari has a habit of running slowly if you have too many bookmarks.