Chosen Solution
Hi there. I think this is the model of my MacBook Pro, these are the specs I found - 15”, 2.3 Ghz processor, mid 2012 with Intel Core i7. I’m no techo so it’s gibberish to me. I still have OS 10.8.5 on my internal hard drive because I still use Compressor and DVD Studio Pro, and have a few Garageband tracks I wish to keep. However, I downloaded Yosemite 10.10.5 onto an external hard drive and have been booting up on that for the last 3 years. So I downloaded Sierra onto another external hard drive thinking I could do the same thing. (I want Sierra so I can update my Premier Pro version). It appears on my desktop as an external drive but when I go to Startup Disk, it doesn’t appear as an option. Is there something technical that prevents me from doing this? (Yes, I might be a bit behind the times but will hopefully be up-grading at year’s end). Any help will be appreciated.
Apple upgraded the file system in High Sierra on SSD drives (APFS). I’m suspecting your system’s installed OS (HFS+) can’t see it as it does not know how to access the newer file system.
