is this just a version issue? Both my iMac and my new 2017 MacBook are running 10.12.5. The iMac's boot drive is an external but that drive won't boot the MacBook. Version on the iMac is 10.12.5 is something like 16F73 whereas the MacBook's is 16F2073 or something like that. Is it correct to assume that the build number for the iMac's install is an older version, not compatible with the MacBook? My understanding is that all current Mac should run HFS+ just fine. If so I guess I'll just wait for 10.12.6 before I archive my boot backup on that iMac.