Getting 10.11 to work on older macs
I had an older mac and needed to have a Mac OS X 10.11 installed on it, it would not run anything newer. For the purposes of this explanation I am assuming you have access to a slightly newer Mac as well, e.g. 2-5 years newer than the target machine. Step 1. get the installer DMG. Open it when it is finished downloading. Step 2 . Install on your own internal hard drive (run the installer and choose your own machine as the target). This creates the installer application in / Applications (even if your OS is newer). This part is not obvious, and surprisingly it doesn't tell you that your machine is too new. Step 3 . Get Etcher from https://etcher.io Step 4 . Attach an external hard drive. Make sure it's empty and formatted HFS+ (use Disk Utility which is in the Utilities folder in your Applications folder ) . You click on the hardware drive shown on the left panel, NOT the partition. Important: tell it to use a GUID partition scheme (popup menu ...