Switch bootcamp partition from MBR to GPT?

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Switch bootcamp partition from MBR to GPT?

A bit of background into what's been happening so far:

Trying to download Windows 10 onto my Macbook Pro (mid-2012, OS Sierra 10.12) through Bootcamp. Everything downloads perfectly, partition goes up perfectly, it's all good.
Open Windows 10. Get error for "no bootable device found" despite the thumb drive I used still being plugged in.
Reboot computer, boot from EFI boot. It works!

So now I've finally booted into Windows 10, but when it gets to the part of the installation where I'm supposed to select the part of the disk I want to install Windows on, when I select the bootcamp partition it says that I can't install Windows on an MBR disk, because it requires a GPT disk instead.

And I have no idea how to switch to a GPT disk.

Pretty much everywhere online says to download the software "gdisk" but I am highly wary of downloading any sort of software from the Internet, so I would prefer to not go that route.

I also saw some advice where someone said to format the partition to "Mac OS Extended (Journaled)" but when I did that, it said that it couldn't download to a disk that wasn't "NTFY" (or NTFS..... honestly, it was 1 AM at this point and my memory is a little foggy).

I've been trying to look for solutions for a solid day, but none seem to be fitting to my particular problem, and I've got no idea how to solve it. Any help would be greatly appreciated.

I've included a screenshot of my specs, if they can help:

MacBook Pro

Posted on Jul 16, 2018 10:13 AM

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Answer 1

Top-ranking reply

Loner T

Level 9

59,536 points

Jul 16, 2018 2:47 PM in response to violetisblue

Your 2012 Mac does not support EFI boot properly. We need to install Windows using legacy BIOS. Your disk requires a Hybrid MBR, which is typically created using GPT FDisk (https://sourceforge.net/projects/gptfdisk/), if BCA fails to do it.

If you do not want to use any third-party utility, run BCA and click on Remove/Restore. Once it is cleaned up, re-run BCA, connect your USB (which has both types of installers - EFI and BIOS) and click on Install. This should create the partition and MBR both. it you still get an error, from macOS Terminal, post the output of

diskutil list

sudo gpt -vv -r show /dev/disk0

sudo fdisk /dev/disk0

Regarding GPT FDisk, see if Upgraded to High Sierra, used Disk Utility, now Windows 10 won't boot allays your concerns regarding utilities from the Internet.

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Answer 2

Loner T

Level 9

59,536 points

Jul 16, 2018 4:13 PM in response to violetisblue

Connect the USB, reboot and hold Alt/Option key. From the Apple Boot Manager, select the Orange Windows icon (not EFI Boot) and try to install Windows.

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Answer 3

Loner T

Level 9

59,536 points

Jul 17, 2018 6:45 PM in response to violetisblue

Insert a blank DVD-R SL, right-click on the W10 ISO, choose Burn and expand the dialog box to look like the following.

Choose the lowest 'speed' to avoid block errors, and burn the ISO. Please ensure that it shows up on the macOS side correctly. If it does, run BCA, and click on Install, do not interrupt the installation. The default is BIOS mode on a 2012 Mac. If you see any GPT or MBR errors, post the exact image. If you see a missing driver dialog, the DVD was burnt improperly. Use the 1607 ISO, not the 1803.

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Answer 4

Loner T

Level 9

59,536 points

Jul 16, 2018 11:56 AM in response to violetisblue

Can you connect the USB to the Mac, and post the output of

diskutil list

from macOS Terminal?

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Answer 5

Loner T

Level 9

59,536 points

Jul 16, 2018 5:38 PM in response to violetisblue

Before you spend more money, can you run BCA and use the Create and Download options to recreate the USB?

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Answer 6

Loner T

Level 9

59,536 points

Jul 17, 2018 11:47 AM in response to violetisblue

Can you use a W10 1607 ISO and try to install Windows?

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Answer 7

violetisblue Author

Level 1

8 points

Jul 17, 2018 4:04 PM in response to Loner T

I was able to download that ISO file through Bootcamp, but when I tried to boot it up and open Windows to install, I ran into the same problem as with the ISO file I was originally using - "no bootable device" when booting from Windows, and "can't install onto an MBR disk" when booting from EFI.

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Answer 8

Loner T

Level 9

59,536 points

Jul 16, 2018 10:58 AM in response to violetisblue

Is your USB a USB3 flash drive? Check in macOS -> About This Mac -> System Report -> USB and check the speed for the specific USB. It should be 480Mbps.

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Answer 9

Loner T

Level 9

59,536 points

Jul 16, 2018 7:49 PM in response to violetisblue

What is the name of the Windows ISO file you are using?

Connect your USB, select these two tasks, point to the Windows ISO

This will recreate the USB Installer.

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Answer 10

Loner T

Level 9

59,536 points

Jul 17, 2018 4:18 PM in response to violetisblue

We cannot use the EFI Boot on a 2012 model. With the USB connected, if you reboot and hold Alt/Option, what are the available selections from the USB disk (Orange icons)?

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Answer 11

Loner T

Level 9

59,536 points

Jul 17, 2018 4:27 PM in response to violetisblue

Does the file structure on the USB look similar to

Specifically, do you see both bootmgr and bootmgr.efi?

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Answer 12

Loner T

Level 9

59,536 points

Jul 17, 2018 4:42 PM in response to violetisblue

Can you post the file structure of the USB, similar to what I have posted?

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Answer 13

Loner T

Level 9

59,536 points

Jul 17, 2018 4:54 PM in response to violetisblue

Connect the USB, and post the output of

sudo fdisk /dev/disk1

I have assumed disk1 is the USB drive. If it is not, change disk1 to appropriate value by looking at the output of diskutil list.

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Answer 14

Loner T

Level 9

59,536 points

Jul 17, 2018 6:01 PM in response to violetisblue

Do you have a blank DVD-R Single Layer disc? Does your built-in Optical drive work properly?

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Answer 15

violetisblue Author

Level 1

8 points

Jul 16, 2018 3:38 PM in response to Loner T

Re-running BCA and creating a new partition didn't work (a fun new error - a blank white screen that lasted for at least five minutes until I just shut down my computer), so here's the terminal output:

If it comes down to it, I'd be willing to install gdisk or fdisk or whatever's needed, but I'm not very tech literate and I have no idea where to even start.

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Switch bootcamp partition from MBR to GPT?

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