Re-install OS after hard drive failure on Mid 2011 iMac
iMac hard drive failed. I need to know the best way to restore the operating system to this computer. How to download the OS and how to connect to the iMac to install it.
Earlier Mac models
Start up from macOS Recovery
Option-⌘-R
Upgrade to the latest macOS compatible with your Mac.
In Disk Utility>View, select Show all Devices, highlight the top left entry.
Run Disk First Aid on all items in the left panel, from top down.
APFS won't work for Sierra or earlier, Sierra or earlier needs MacOS Extended Journaled. High Sierra won't work for APFS on earlier Macs.