Sonoma and Windows 10 on an iMac 27” 5K late 2015 (17,1)
Successfully got the above running and wanted to document how I did it for others and for future me.
Hardware:
iMac 27” 5K (late 2015), 4 GHz Quad-Core Intel Core i7, 16GB RAM, AMD Radeon R9 M395X 4GB.
4TB Internal SSD SATA (Samsung 870)
2TB Internal PCIe NVMe SSD (Samsung 980 Pro)
Beginning state:
NVMe Drive as startup disk, running Mac OS Monterey. Wife and kids found it “unusable” due to freeze-ups and frequent crashing.
250 GB Bootcamp partition running Windows 10, mainly for my son’s games. Getting full.
Motivation:
Minimal goal was to make the Mac more “usable” and less crashy, so I thought I’d try downgrading to a more stable Mac OS version (wasn’t sure if the frequent crashing and slowness was due to Monterey or the third party Samsung NVMe SSD, or both or neither).
End state:
Partitioned the 4 TB Internal SSD SATA into two parts:
A 3.0 TB startup disk with Mac OS 14.2.1 Sonoma (enables the “Shared Photo Library” in the Photos app so my wife and I can share a consolidated photo library!)
A 1.0 TB partition running Windows 10. (More room for my son’s Windows games.)
(The 2 TB NVMe SSD remains unchanged. Trouble-shooting or re-using it is a future project; for now the internal SATA SSD is fast enough and not crashy.)
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How I did it:
Online, there seemed a consensus that Mojave was the optimal OS for Intel Macs in terms of stability, so I downloaded Mac OS Mojave installer from the Mac App Store, got a USB drive and made a bootable nstaller using these instructions from Apple.
(How to create a bootable installer for macOS)
https://support.apple.com/en-us/101578
I wiped the Internal SSD SATA drive and held option key during restart, then installed Mojave using the bootable installer. Success! Mojave running clean and fast. Minimal goal achieved.
Next I got greedy and decided to try and jump all the way to Sonoma (unsupported on my late 2015 iMac) using the Open Core Legacy Patcher. (OCLP).
https://dortania.github.io/OpenCore-Legacy-Patcher/
(I’d been wanting the shared photo library feature in Photos for a while, so my wife and I could consolidate our separate photo libraries, but that feature was in Ventura and later, and my Mac was unsupported for anything later than Monterey. )
I followed the excellent OCLP instructions and got Sonoma installed and working, and was impressed at how fast and smooth it ran on my 8 year old machine. (An existence proof for Apple’s unnecessary planned obsolescence.)
However, last step was to install Bootcamp and get a bigger Windows partition. And that’s where things got tricky.
I first tried the standard install using Boot Camp Assistant in Sonoma. It seemed to go fine on the Mac side, but then when I rebooted to start the Windows Installer, I got the “blue screen of death” (BSOD) saying “Your device ran into a problem and needs to restart. We’ll restart for you.” Stop code: SYSTEM_SERVICE_EXCEPTION, What failed: win32kfull.sys.
Tried that again with the same result. I figured it must have to do with the fact I was running unsupported Sonoma using OCLP. So I went to the OCLP guide and found the step by step instructions to install Windows in UEFI mode:
https://dortania.github.io/OpenCore-Legacy-Patcher/WINDOWS.html
Went through that whole process, only to get the same BSOD with the same SYSTEM_SERVICE_EXCEPTION, win32kfull.sys error.
So I googled around and found two separate threads (one reddit, one macrumors) that suggested this could be solved if you go back to a supported Mac OS version, use Boot Camp Assistant to install Windows, get that stable, AND THEN use OCLP to upgrade just the Mac OS partition to get back up to Sonoma. Both threads said that worked, so I went ahead and started over: Re-made my Mojave bootable installer, wiped the internal SSD SATA drive, installed Mojave, used Boot Camp Assistant to install Windows 10 (1 TB Windows partition, leaving me 3 TB for Mac OS), and made sure the graphics card drivers were installed and working in Windows and that the games ran fine.
Then I went back to Mojave and used OCLP to install Sonoma again.
This process took a LOT of rebooting to finally get Sonoma working smoothly. But finally got it running smoothly, and had to use the extra “Moving OpenCore from USB to macOS Drive” instructions to get the machine to boot into Sonoma without needing the USB drive plugged in.
https://dortania.github.io/OpenCore-Post-Install/universal/oc2hdd.html#grabbing-opencore-off-the-usb
Anyway just wanted to document the process and resources so I can remind myself when I inevitably need to mess with it in the future. But for now it’s time to enjoy my 8 year old Mac interacting with my iCloud accounts and photos sharing for my family. Avoiding buying a new computer for another year or two, I expect. (Plus the Silicon Macs apparently can’t run Windows native enough for PC gaming anyway. Part of me is thinking I should just start collecting 2019 and 2020 iMacs. Handy to have native Windows and yesterday still be able to run Sonoma!)
