Error when installing Windows 8.1 on 27-inch Mid 2011 iMac

Hi,

This is my first post here so please be gentle 🙂

I have a 27" Mid 2011 iMac running High Sierra (10.13.6) and only last week I read an article stating that you can actually install Windows on an Apple machine. That made me interested and now I am determined to install Windows 8.1 on it. What I thought was going to be an easy task, has escalated into a very tedious and nerve wrecking process as I keep stumbling upon new errors.

There is one internal HD in my Mac of 1TB. The size of the Windows partition does not really matter that much to me, although probably the bigger the better, as I may end up just using Windows.

I used Bootcamp (v6.1.0) to create the partition (the latest/current one I created is 500gb for Windows). I downloaded an ISO from the Microsoft website and also bought a valid Windows 8.1 license key. Initally I used a USB3 stick, but read that USB2 is needed which I received this morning. The stick contains the ISO and install files, all created by Bootcamp.

Once Bootcamp is done with formatting etc, the Mac restarts and I then get the infamous black screen stating "No bootable device - please insert disk and press any key". I can get around that by holding down the Option key during a reboot, allowing me to select the EFI Boot (the other two options are the OS and Recovery).

Once selected the Windows setup starts, but I get stuck during the partition selection screen where Windows asks me where I want to install it.

In that screen I see Disc 0 with partitions 1-4 (I have no idea where the other three partitions are coming from, I never made them and am the first owner of this Mac). Partition 4 is the one that Bootcamp created. Windows lists a few errors and allows me to format the partition. But even when it is formatted I see this error:

"Windows cannot be installed to this disk. The selected disk has an MBR partition table, On EFI system window can only be installed to GPT disks."

After that I am stuck and need to abort the installation process.

I have read solutions about using SHIFT + F10 and using some commands during the Windows install to change the format, but I'd rather not do that as I expect that I will wipe my whole OS since you can only use this cmd for the whole disk, not a partition.

I also read about another process which you can do in OS to change from MBR to GPT which may not cause data loss, but I lack the knowledge to really understand that process and its impact.

I have done a PRAM reset which was once hinted in an older topic (so remove the Bootcamp partition, do a reset, create a partition and try again), but to no avail.

I have made sure to disconnect all my external HD's, have no other USB devices attached to the Mac apart from a mouse and keyboard.

So right now I am stuck and am starting to think if I should maybe just clear the whole HD (I have a backup created by time machine), set it to GPT and install Windows. I however would not know how get the OS back (never done that). On top of that, I read that older Macs may need to do the Windows install from a DVD, not from USB. If so, my internal SuperDrive may be broken as it cannot read a DVD with the ISO file that I created using an external burner. It only prompts the Burn app and Burn indicates that there is no disc. So I don't want to end up wiping my whole HD and then finding out that I cannot install anything because of a broken SuperDrive.

So right now my main question is, how can I solve the error shown in red so I can continue with the installation?

Sorry for the long story, but I hope it has captured everything that is needed to make a good assessment.

Thx,

Ron