iMac 21.5 - Late 2013 - running latest version of Sierra Continual beach ball for nearly every application and utility. Very annoying. Here is what has been tried: DriveDX indicates HDD is healthy Performed an re-install of OS Sierra - made no difference. (old data and apps were retained) Activity monitor - all processes appear to be normal. EtreCheck found system performance was "poor" but did not report anything that stuck out. Possible Issues HDD Fan speed utility reporting fan speed as "RPM -1". But, no evidence of overheating. Over 250GB of data stored on various desktop folders - could this be a problem? Really mystified as to the root cause. Your help or any suggestions would be much appreciated.