Answer: The archived system files of a previous system are located in /Library/SystemMigration. You can delete the folder (saved me 800 MB), but it may not work if you had a previous beta installation of El Capitan. In this case you need to turn off System Integrity Protection temporarily or delete the folder remotely from Recovery or a previous OS X installation. --- I know that upon installation, the system installer moves everything in protected locations (e.g. /System, /bin, /sbin/, /usr) that doesn’t belong there to another location. My question is: where? I came across two suggestions: /Library/PreviousSystems /Library/SystemMigration I only have the latter folder, so I don’t know for sure. I’m asking this, because I’m doing some housekeeping and would like to remove the stuff I don’t need anymore. Just curious where the files end up.