Running Windows through External HD on Mac
An EFI boot manager utility
Status: Beta
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Hi guys. I've been able to install windows 10 Enterprise on my External drive. It boots up fine on my pc, but once I plug it into my Macbook Pro (Early 2015), it is not seen as a bootable device. I've installed rEFInd as well, and when I try to load Windows, it gives me the error:
Starting legacy loader
Using load options 'USB'
Error: Not Found while loading legacy loader
Please make sure that you have the latest firmware update installed.
Hit any key to continue
Please provide any insight to this problem. This is my first Mac based system, so please explain in the simplest terms possible. Thanks you.
BIOS-mode booting from external drives was flaky in rEFIt (rEFInd's predecessor) and remains flaky in rEFInd. Apple just keeps changing the details of how BIOS-mode booting works, which makes it impossible for a single developer with access to just a couple of Macs to keep up with it. You might have better luck with an EFI-mode install, but that would require your PC to support EFI-mode boots.
It also occurs to me that you might have an EFI-mode install, but if Windows put the ESP on the original computer's internal disk, there will be no way for that installation to boot on anything but the original computer. The ESP must reside on the external disk in order for such an installation to be bootable on multiple computers.
Finally, I'm not sure that what you want to achieve is really achievable, no matter what the boot mode. The reson is that Windows installs lots of system-specific drivers, so if you move an installation from one computer to another, Windows will end up spending a lot of time updating drivers for the new host. At best this is likely to take a long time, and at worst it will fail and leave you with an unbootable Windows. If you move a disk back and forth between two computers, I expect that process would repeat with each move. I can't say I've actually tried this myself, but I'd be surprised if it could be made to work reliably. The exception is if it's not a regular installation, but instead something designed as an emergency disk. (There are tools to help create such disks, but I don't have any references, offhand.) Such disks rely on lowest-common-denominator "generic" drivers rather than drivers for specific hardware, so they're limited in their capabilities but are useful for tasks such as emergency recovery or OS installation.