Quote:
Originally Posted by helpplease
Hi,
@odamizu
I tried to boot off my old SDD harddrive in an external caddie (running high Sierra 10.13.6) from new MacBook Air (shipped with Catalina), and it refused to allow it ...
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Quote:
Originally Posted by pwalker8
As a rule of thumb you can't run a machine on a IOS version prior to when the first model of that machine was shipped. Mostly, it's a situation when the older IOS version doesn't have the device drivers needed for the newer hardware. Thus I can boot my old mac mini and iMac on an external drive with Sierra on it, but not my 2018 macbook pro. I tried the same thing that you did (but with Sierra) and got the same error.
I understand there are hacks you can do to force it to try, but I suspect you may run into so odd issues. For me, it wasn't worth the effort. I can book my iMac on an external drive with Sierra, which suits my needs. If you really need to run High Sierra, then you might consider getting an older machine. I'm not sure what incompatibilities you are running into.
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I think pwalker8 is correct.
I was taking a Mac that shipped with High Sierra and used an external SSD to boot it with Catalina. I've not tried the reverse.
Also, from Apple: "
The version of macOS that came with your Mac is the earliest version compatible with that Mac."
Have you considered a VM? That is supposed to work.