Quote:
Originally Posted by odamizu
1) If I have High Sierra installed on my Mac and I install Mojave on an external drive, what exactly would be installed on the external drive? Just the System folder? Then the external drive would share the Applications, Library, and Users folders with my Mac? Wouldn't there be a risk of adverse effects and incompatibilities between the two systems?
2) If Apple releases a software update for Mojave, which is on the external drive, how would that work? Would I be alerted the next time I booted from the Mojave drive and the update would be applied to Mojave without affecting the High Sierra system on my Mac?
I am risk-averse and don't want to do anything that might mess up my primary Mac.
Thank you
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Before you do anything at all that impacts your mac, do a time machine backup. Then clone your iMac hard drive to an external drive - ssd is best as it will boot and run almost as fast as your internal drive. The clone will be bootable, and it will also allow a complete restore to your internal hard drive should that ever be required.
Now you can install another OSX to another external drive. This will boot into a completely separate osx system. It will see your internal drive as a separate Mackintosh HD. You can safely install apps and operate the external you are booted into without it impacting your internal one. You can see the files in your internal hd as it is treated and mounted like any other attached drive. So drag and drop is fine, but installing etc is confined to your booted drive. If you are a different user in the external boot drive then permissions will likely impact access to your internal files when booted into that external drive. I haven't used that scenario, only as the same user in all drives.
I have an 2019 500gb ssd iMac with Mohave installed. I cloned it to an external samsung ssd. Then I booted the ssd clone and basically treated it as my second iMac. It meant I had to update mohave twice - once when booted into the internal ssd, and again when booted into the clone ssd. I use the clone to test apps like the latest sigil to see how it would look and run compared to the earlier version.
I think if you clone your internal drive, boot into it, then update the osx to that drive it would work for you to test mohave and catalina.
Actually I am so paranoid, I have 2 clones on separate ssds. If one fails I have another one to boot into.