Boot Camp & Win 10 on a 21.5" Retina 4K iMac?

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Boot Camp & Win 10 on a 21.5" Retina 4K iMac?

I got a lovely new 21.5-inch iMac with Retina 4K display last week, bumped up with a Core i7, 16GB RAM, and a 512GB Flash drive 🙂

I previously had Windows 10 installed on my old 21.5" iMac, which was a 2011 model (the last of the "fat" ones before the 2012 slim down). I successfully installed it using Boot Camp 5.something (whatever the latest version was before Boot Camp 6) despite it not being officially supported.

I have tried to use Boot Camp 6 to install Windows 10 on my new iMac, but it just won't work.

I understand that according to the Boot Camp page at Apple.com, the new "Late 2015" 21.5" 4K and 27" 5K iMac models are not listed as being compatible (with any Windows, not just 10). I had hoped that was just because the page hadn't been updated yet... but I guess that's not the case? 😟

The first time I tried BCA6, it got as far as the actual Windows installation, but the Windows installer then refused to install Windows 10 to the Boot Camp partition, even though I had used the installer to format it to NTFS, exactly as the instructions tell you.

I ran BCA6 again to remove and recreate the partition, and tried again... this time I didn't even get as far as the Windows installation - BCA6 errored out, complaining that it could not download the support software.

Tried again... same thing happened.

Any ideas? Should it work, and something has gone wrong, or is it that it really is not yet supported?

Has anyone else managed to install Windows 10 on a late 2015 21.5" 4K iMac?

iMac (Retina 4K, 21.5-inch, Late 2015), OS X El Capitan (10.11.1)

Posted on Nov 7, 2015 12:03 PM

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Answer 1

Loner T

Level 9

59,471 points

Nov 7, 2015 4:33 PM in response to mattdodd

Please use a wired connection to the Internet and try BCA again. Your 2015 iMac supports W10. The Apple pages have not been updated yet. Many have installed W10 on the 5K and 4K iMacs.

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Answer 2

mattdodd Author

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Nov 8, 2015 8:50 AM in response to Loner T

I'm already using a wired connection, and have tried three times so far.

First time failed at the Win 10 installation stage, as it could not install to the Boot Camp partition despite it being formatted as instructed.

Second and third times failed to even download the software when running BCA6 in OS X.

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Answer 3

Loner T

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Nov 8, 2015 9:00 AM in response to mattdodd

Do you see an OSXRESERVED partition if you run diskutil list from OS X terminal?

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Answer 4

mattdodd Author

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Nov 8, 2015 9:38 AM in response to Loner T

Nope. Should there be?

Are you sure that the new Late 2015 4K and 5K iMacs are supported, even though Apple's own site makes no mention of them?

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Answer 5

Loner T

Level 9

59,471 points

Nov 8, 2015 10:15 AM in response to mattdodd

If they were not supported, Bootcamp Assistant would not be installed on the Machine. 😉

OSXRESERVED is the new USB replacement for EFI booting the 2015 Macs.

Your 2015 Macs are UEFI-compliant, and do not really need BC Assistant or drivers to install Windows. You can directly boot from a W10 Installer USB flash drive downloaded from Microsoft and point it to a Disk Utility-created Free Space partition to start a W10 installation. You can try the direct method as a test.

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Answer 6

mattdodd Author

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Nov 8, 2015 12:39 PM in response to Loner T

Doesn't creating a bootable USB installer for Windows 10 require an existing installation of Windows, though? I have no access to a Windows machine.

(Although I do have a bootable DVD I created from when I installed Windows 10 on my old 2011 iMac.)

Can Disk Utility create a new partition without losing existing data, or is the only way to do that to use Boot Camp?

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Answer 7

Loner T

Level 9

59,471 points

Nov 8, 2015 1:02 PM in response to mattdodd

Back up OSX. Use DU to create a Free Space partition. It will leave your existing partitions intact. You can download a USB Installer from M$ and boot from it. You can try a external DVD of W10 to boot from, but ensure that the DVD drive supports booting.

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Answer 8

mattdodd Author

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Nov 8, 2015 1:37 PM in response to Loner T

The Windows 10 media creation tool from Microsoft requires Windows. And as mentioned previously, I have no access to an existing Windows machine.

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Answer 9

Loner T

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Nov 8, 2015 2:23 PM in response to mattdodd

1. Does BCA give you an option to create a USB?

2. Do you have an external Optical drive?

3. The following is slightly convoluted method.

a. You can download VirtualBox, install W10 in VirtualBox (do not activate W10).

b. From this test installation, create a USB Installer.

c. Use DU to create the partition.

d. Install using EFI.

e. If everything is working, remove the W10 VM, and test.

f. You can always use VirtualBox to import the BC/W10 as a VM, if desired.

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Answer 10

mattdodd Author

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Nov 8, 2015 3:24 PM in response to Loner T

1) No. Boot Camp 6 does not have the option to create a USB installer, unlike past versions (at least not on my late 2015 iMac). All it lets you do is set the partition size and point it at the ISO.

2) I can borrow my wife's SuperDrive if necessary (she has one for her rMBP).

3) That does sound rather convoluted. What happened to "It just works"? 😟

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Answer 11

Loner T

Level 9

59,471 points

Nov 14, 2015 9:56 AM in response to mattdodd

mattdodd wrote:

2) I can borrow my wife's SuperDrive if necessary (she has one for her rMBP).

😟

The Superdrive and your Windows DVD should work to install via EFI boot. It just works is valid for Apple software. 😉. It does not apply to Windows software on any machine. 😁😝.

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Answer 12

mattdodd Author

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Nov 8, 2015 4:07 PM in response to Loner T

OK, cool. I'll give it a go using Disk Utility for the partition and Superdrive + DVD for the installation.

What about the Apple Boot Camp drivers/software, though? Wouldn't the iMac still need that?

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Answer 13

Loner T

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Nov 14, 2015 9:56 AM in response to mattdodd

The BC drivers can be manually downloaded and installed after Windows is up and running with generic drivers.

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Answer 14

mattdodd Author

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Nov 8, 2015 6:18 PM in response to Loner T

How do you do that?

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Answer 15

Loner T

Level 9

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Nov 8, 2015 6:48 PM in response to mattdodd

From the OS X side, run BC Assistant and download the Windows Support Software. It should give you version 6.x drivers. You can check the version in Bootcamp.xml on the USB and look for a line which contains the Product Version.

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