How to create a dual-boot system on late-iMac with Monterey on External SSD?

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How to create a dual-boot system on late-iMac with Monterey on External SSD?

I have a Late-2015 27" i5 iMac currently running Catalina. It's qualified for Monterey and I'd like to install Monterey on a bootable external SSD (preferably ending up with a dual-boot system).

I recollect seeing information in the past that you must first upgrade the internal drive to Monterey before you can install Monterey on an external drive. Is that the case? Must I upgrade the internal drive first?

[Re-Titled by Moderator]

Earlier Mac models

Posted on Mar 20, 2024 2:36 PM

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Answer 1

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BDAqua

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Mar 20, 2024 3:32 PM in response to MartinR

Nope, my Internal drive has Catalina, I can boot from Mojave, Big Sur, Monterey, Ventura, or Sonama on external SSDs or HDDs, just requires holding Option key o startup if Startup Disk panel doesn't se the other bootable drives.

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Answer 2

MartinR Author

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Mar 20, 2024 6:09 PM in response to BDAqua

Thanks. This is the start of a two-step process. After installing Monterey on the external SSD, I intend to open the iMac and replace the internal HDD with the SSD. I want the SSD to be bootable before I do the surgery. It will be an adventure.

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Answer 3

MartinR Author

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Mar 21, 2024 5:39 AM in response to BDAqua

I seem to have built up an excess of older Macs over the years and wanted to give this upgrade/repair a try. Some years ago I opened a 24" iMac to replace the PRAM battery and I was able to do it just by lifting the screen off the base, not actually removing it. It was fiddly and a tight fit but I did it. This time I know I have to remove the screen on the 27" iMac and I'm intrigued by the adventure. I'll be using a kit from iFixit. If it doesn't work out I will have learned some things and will not consider the iMac lost. But I may breathe new life into that iMac!

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Answer 4

Mar 21, 2024 8:20 PM in response to MartinR

Make sure to keep the Display Assembly vertical since the display can crack under its own weight. A co-worker found out about this the hard way.....I still remember hearing the crack from the display snapping while it was sitting flat on the table.

Good luck & let us know how you make out with the upgrade.

Edit: I also recommend not installing the adhesive strips (at least don't peel them from the front side) until you confirm the SSD upgrade works when installed internally. I use some painters tape or even packing tape to hold the display in place & trying to keep the display tilted back.

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