I'm running a mid-2010 iMac with an i3, 12GB ram, & factory 2TB HD with 10.9.5. I upgraded from Snow Leopard to Mavericks 10.9.5 almost 18 months ago by utilizing a Carbon Copy Cloner backup and doing a full wipe and clean install on my iMac hard drive. The computer has performed great until the last few months and has experienced major slowdowns and excessive beach balls. I have NOT performed any other major updates since then. I cannot think of one item I have added or changed to initiate the slowdown, but it has gotten to the point that everyday tasks are becoming hard to do. Three weeks ago Safari became unstable and would crash after sitting idle overnight. An update to 9.0.3 has solved this issue (I was at 7.x.x). There doesn't seem to be anything in Activity Monitor and when idle, CPU usage is minimal. Something needs to happen and it doesn't need to be a new $3k iMac! Where do I need to start looking?