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I have an installation of windows 8 on an external hdd. When I try to update to windows 10 the update fails with the message that windows on usb drives cannot be updated. Is there a way to update this portable windows installation?

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My laptop came with windows 8 pre-installed. I swapped the drive for an ssd and installed linux which I use mainly. To be able to use windows I followed the instructions given in the answer to this question.

I was not able to update windows on the external drive (the update failed with the message that "windows to go" could not be updated. I then revered the changes in the registry (see linked question). But still I was not able to update - it failed with the same message.

Then I found an additional registry setting in:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control

I changed the value PortableOperatingSystem from 1 to 0 and the update succeeded.

After the update I had to add the value PortableOperatingSystem, it was removed from the registry. Give it the value "1". Then, shutdown windows (do not use hibernation, press SHIFT while clicking shutdown), remove the drive and mount it with another operating system so you can apply the changes in the linked question (BootDriverFlags 0x14).

After this steps I was able to boot windows 10 from the external drive.

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    Very interesting. I was already able to boot from USB2 port (I have USB3-capable adapter) without this 'PortableOperatingSystem' key. I tried creating this key (which didn't exist in my registry) and setting it to 1 (it is DWORD by the way), but it didn't help with USB3 booting of Windows 10 drive copy - I still get 'INACCESSIBLE_BOOT_DEVICE' error. I think there is some problem with USB3 driver at boot time. I have already set BootDriverFlags to 0x14 (I believe it is 0x04 to enable USB2 and 0x14 to include USB3). :-(
    – gogoud
    Jul 27 '16 at 21:19

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