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Question: Downgrade Mac OS on last iMac 5K 27"

Hello


I will command a new iMac Retina 5K 27" with High Sierra installed. (Buy iMac - Apple)

Could you tell me if it possible to downgrade this kind of machine to Sierra ? Is it compatible ?


Regards

iMac, macOS High Sierra (10.13.1)

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Because Mac's require a specific build versions and the older version does not support the new Mac.

see > Use the Mac operating system that came with your Mac, or a compatible newer version - Apple Support


You might be able to install the previous macOS version onto an external drive and get it to work. But because of macOS's (EFI, Recovery and Container) complexity, I would not recommend forcing it onto or even into a partition on the internal drive.

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Nov 13, 2017 12:39 PM in response to vghilardi In response to vghilardi

Because Mac's require a specific build versions and the older version does not support the new Mac.

see > Use the Mac operating system that came with your Mac, or a compatible newer version - Apple Support


You might be able to install the previous macOS version onto an external drive and get it to work. But because of macOS's (EFI, Recovery and Container) complexity, I would not recommend forcing it onto or even into a partition on the internal drive.

Nov 13, 2017 12:39 PM

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Nov 13, 2017 9:01 AM in response to vghilardi In response to vghilardi

Can you tell me why before it was possible to do that and what is preventing it today?

Can you put a date to "before?" I've used Macs since before 1990 and don't recall that being possible with the majority of models.


Also we are all end-users like you and have no insight into Apple's notoriously secret decision process and policies, so "why" can't be answered here without speculation, which the forum Terms of Use forbid.

Nov 13, 2017 9:01 AM

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Question: Downgrade Mac OS on last iMac 5K 27"