I have a 2013 MacBook Pro Retina with both macOS and Windows 10 installed on the internal SSD. I regularly put my MacBook into Target Disk Mode and boot into the macOS partition via a 2015 iMac.
My question is, is it possible to boot into the Windows partition via the same method – by putting my MacBook into Target Disk Mode and booting into the Windows partition via the iMac?
Things I've tried:
When I hold alt on boot to access the Startup Manager on the iMac, I do not see the Windows partition as an available boot disk.
I have attempted to boot into the MacBook macOS partition via the iMac, and then change the startup disk via the Settings panel and restart. This seemed to work, and I was able to boot into Windows and see the Windows 10 loading wheel, but I was then presented with the Windows error 'INACCESSIBLE_BOOT_DEVICE', which I can't seem to get past.
Any advice would be very much appreciated.
Best Answer
Let me try to explain what is happening.
The MacBook Pro is put in Target disk mode. At this point, the MacBook Pro is running software (firmware) stored on the logic board. This software is provided by Apple.
The iMac boots. At this point, the iMac is also running software (firmware) stored on the logic board. This software is also provided by Apple.
The iMac recognizes the MacBook Pro as an external drive and determines the default operating system to boot is on this drive.
The iMac reads the necessary file from the hidden EFI partition on the MacBook Pro. This file is loaded into the memory on the iMac and executed. This file is provided by Microsoft.
The executing program from Microsoft now running on the iMac has no idea what Target disk mode is and no idea how to communicate with the MacBook Pro using the cable connecting the two computers together.
So you may see Windows start to boot but in the end Windows can not read additional files from the MacBook Pro.
There is no solution to this problem, but even if there was, Window still would fail to boot. Windows is licenced on a per computer basis. So at some point later in the boot sequence, Windows would have determined the computer was an iMac instead of the MacBook Pro. Windows would then have produced an error message and halted.