I find these threads with same problem: http://forums.macrumors.com/threads/at-my-wits-end-with-my-beachballing-imac-sug gestions.1956948/ http://forums.macrumors.com/threads/beachballing-after-any-action.1956503/#post- 22572555 I have iMac late 2012 (CPU i5 2,7 GHz, RAM 8GB, HDD 1TB 5400) with OS X El Capitan. For all the time I did not do a clean install of system. In last months I have problem with smoothness of system. System very offten (every 1-10 minutes) loading - beachballing. In "loading mode - beachballing" are: mouse cursor is rolling - beachballing music from iTunes stop play for a while video in VLC stop play for a while I can do nothing at this time Last week I made clean install of OSX (El Capitan) with format HDD. After install, system gone smootly for few days. Then I copied some files from backup (maybe 100GB of itunes media) and next day system was very slow. After reboot or wake up mouse cursor still rolling (beachballing) for 5-10 minutes and then after every operation (every mouse click) cursor rolling (beachballing) from 10 seconds to 5 minutes. I couldn't do nothing. Therefore I made clean install again 2 days ago and system go smooth again - still without my data from backup, only clean install without thirt party apps and data. I tried Apple Hardware Test (AHT) before boot. Everything was OK. I tried some diagnostic tools for test HDD and system (DriveDx, EtreCheck). DriveDX find some problem with sector on HDD with SMART, but I don't know if it is that problem. I send report from EtreCheck: After clean install without solution, I thing that problem is in HDD or RAM. It means, I must go to service. Before that I woult like to know, is it really HW problem. Do you have any idea, where is problem and how I find/fix it? I will be very happy.