I've got a 500 GB HDD in a late 2012 Mac Mini. I'm in the process of upgrading it to a 1 TB hybrid (fusion) drive.
The original 500gb drive was running OSX 10.8.5 and I copied the drive in its entirety using Carbon Copy Cloner to the 1 TB drive.
I had the 1 TB drive in an enclosure and wanted to test if it would boot so I plugged it into a nearby machine (as the late 2012 Mac Mini wasn't reassembled yet). The nearby machine was a current version Mac Mini purchased about 3 months ago running OSX 10.11.
When I booted into the external drive by holding down the option key I got a grey error screen with a no entry logo (see image below).
Slightly panicked, I reassembled the late 2012 Mac Mini and tried to boot the external 1 TB drive. This time it worked.
Was the issue with the 1 TB drive and / or that the OS didn't copy properly via Carbon Copy Cloner, and I just got lucky when I booted it on the late 2012 Mac Mini?
Or is it an issue to do with the new Mac Mini not booting a 10.8.5 OS?
(Just want to be sure because if it's an issue with the drive or copy of the data I've put on there I want to rectify it now, before I start using this drive in production.)
Best Answer
No Mac will boot to an OS older than itself, with very few exceptions, such as machines released right on the cusp of a new OS release.
The drivers for it simply weren't yet invented.