Upgrading Windows 8.1 to 10 on a late 2015 iMac via bootcamp

I'm in the process of trying to wrangle Windows 10 onto my iMac. The process that I've seen suggested is to install Windows 8.1 with bootcamp then upgrade it to Windows 10 to avoid problems associated with directly installing Windows 10.

I've successfully installed an unactivated copy of Windows 8.1, but I'm stumped as to how I upgrade to Windows 10. When I try the official Windows 10 installation tool, the installer asks for a Windows 10 product key because "Windows isn't activated on this PC". I don't have any product keys.


Any help y'all can provide would be greatly appreciated.


Model: iMac Retina 5K, 27-in, late 2015.

OS: OS X El Capitan, Version 10.11.6

Processor: 3.2 GHz intel core i5

Memory: 8 GB

Storage: 1 TB Sata disk total, 152 GB of which is currently partitioned into Bootcamp.

iMac Line (2012 and Later)

Posted on Apr 6, 2020 03:31 PM

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Question marked as Top-ranking reply

Posted on Apr 7, 2020 01:57 PM

Part of your issue seems to be related to El Capitan (10.11.6). Newer W10 ISOs do not work well, and cause issues on this macOS version. I use Sierra (10.12.6) or Mojave (10.14.6). High Sierra (10.13.6) and Catalina (10.15.x) have issues.


If you have successfully installed W8.1 and left it unactivated, when you try to upgrade W8.1 -> W10, the expectation is that you have bought a valid W10 Product Key from Microsoft Store and provide as part of the upgrade process.


If you try to clean-install W10, you will have 30 days to buy a license and activate it, otherwise Windows Update will not work, which may be acceptable to you.

5 replies
Question marked as Top-ranking reply

Apr 7, 2020 01:57 PM in response to Ventilation

Part of your issue seems to be related to El Capitan (10.11.6). Newer W10 ISOs do not work well, and cause issues on this macOS version. I use Sierra (10.12.6) or Mojave (10.14.6). High Sierra (10.13.6) and Catalina (10.15.x) have issues.


If you have successfully installed W8.1 and left it unactivated, when you try to upgrade W8.1 -> W10, the expectation is that you have bought a valid W10 Product Key from Microsoft Store and provide as part of the upgrade process.


If you try to clean-install W10, you will have 30 days to buy a license and activate it, otherwise Windows Update will not work, which may be acceptable to you.

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Upgrading Windows 8.1 to 10 on a late 2015 iMac via bootcamp

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