Windows 10 won't boot with EFI enabled

Discussions about using Windows guests in VirtualBox.
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Mark92630
Posts: 31
Joined: 2. Dec 2012, 09:56
Primary OS: Mac OS X other
VBox Version: OSE other
Guest OSses: Windows 10

Windows 10 won't boot with EFI enabled

Post by Mark92630 »

My Win10 guest boots perfectly without EFI, but when I enable EFI in VM Settings, the guest gets stuck in the boot up sequence. In the second screen I show below, anything I do eventually takes me back to the first screen.

Is anyone able to get Win10 to boot on macOS Catalina with EFI enabled?

TIA,

Mark
Attachments
First screen I see when trying to boot
First screen I see when trying to boot
Screen Shot 2021-10-16 at 22.08.21.png (101.37 KiB) Viewed 4997 times
Second screen I see, if I try to <exit> the first screen
Second screen I see, if I try to <exit> the first screen
Screen Shot 2021-10-16 at 22.08.44.png (64.78 KiB) Viewed 4997 times
BillG
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Posts: 5102
Joined: 19. Sep 2009, 04:44
Primary OS: MS Windows 10
VBox Version: PUEL
Guest OSses: Windows 10,7 and earlier
Location: Sydney, Australia

Re: Windows 10 won't boot with EFI enabled

Post by BillG »

I don't use UEFI mode for my vms, but from my experience with physical PCs you can't just switch modes and expect it to boot. Machines using legacy boot use the old MBR format for their discs but UEFI requires GPT. I suspect you would need to convert your existing virtual hard drive, or at least the partition which has the Windows boot loader on it, to GPT.
Bill
mpack
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Re: Windows 10 won't boot with EFI enabled

Post by mpack »

What Bill said. If you want to enable EFI you need to do it before you install Win10. In fact just about everything on the motherboard should be decided before you install an OS.

There may be a way to migrate the Windows image using Macrium, see here: https://kb.macrium.com/KnowledgebaseArticle50151.aspx. You'd have to revert the VM settings to make a bootable VM, boot it and make a Macrium backup, then modify the VM settings and try the Macrium restore.

Of course a VM backup would be a good idea before trying this.
The Raven
Posts: 82
Joined: 18. Aug 2016, 20:43

Re: Windows 10 won't boot with EFI enabled

Post by The Raven »

You can use the mbr2gpt tool which is included in Windows 10 - I've used it a couple of times
whilst testing UEFI. It works fine. See description here
https://docs.microsoft.com/en-us/window ... mbr-to-gpt

It's not really designed to be used on a running system so just boot your VM with a Windows 10 ISO.
Instead of following the install route, take the repair option and then go into the command prompt and
use mbr2gpr from there. Once the system disk is converted, select UEFI in the VM definition and it
should start correctly.
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