I was until recently running Windows 7 on my PC, I upgraded to Windows 10 and I know that it can support full UEFI (i.e. with CSM disabled). I believe my PC will be better with CSM disabled, so I would like to disable it (in fact it has to be disabled to boot on to my second drive with Fedora 22 because of the way I installed it).

However, if I disable CSM my drive with Windows on isn't bootable. I can disable CSM and boot off the DVD I made in Windows 7 and install from that, but it doesn't accept my 7 license key when doing this.

I tried using the repair function on the Windows 10 DVD to see if that would allow me to repair the install and make it UEFI compliant, but that didn't get me very far.

Is there any way to convert a traditional disk to a UEFI compliant disk? I don't believe I can extract the Windows 10 key from my upgraded version, but if I am wrong please educate me! I read that once upgraded you can do a clean install of Windows 10, it will recognise the hardware, but I guess once CSM is disabled it doesn't recognise it as the same hardware.

I know I can set CSM to automatic for now to be able to boot to both (I hope I can at least!) but ideally I want a native UEFI installed Windows 10.

The last option I can think of is to pay Microsoft (which I would rather not do!) for a Windows 10 key...

Can anyone make any better suggestions?

1 Answer 1


First, you should understand what's going on: A computer boots by running its firmware code (BIOS or EFI), which in turn runs a boot loader program stored on the hard disk. The boot loader relies on features of the firmware (BIOS or EFI), and so is tied to the firmware type -- you can't run an EFI boot loader under BIOS or vice-versa. There is one partial exception to this last point, though: Most EFIs include a Compatibility Support Module (CSM), which is a sort of BIOS emulator. The CSM enables you to run BIOS boot loaders from EFI, much like WINE lets Linux users run Windows programs.

Thus, switching the CSM on or off will not, by itself, make the computer boot in the desired mode; you must also have a suitable boot loader installed on your hard disk. There can be other complications, too. Switching on the CSM doesn't always disable EFI-mode booting, so you might still end up booting in EFI mode even with the CSM enabled.

A further complication is that Windows ties its boot mode to the partition table type. Specifically, Windows will boot in EFI mode if and only if the boot disk uses GPT; and it will boot in BIOS mode (or using a CSM) if and only if the boot disk uses MBR. Thus, in the case of Windows, switching from one boot mode to another requires changing the partition table type, not just installing a new boot loader.

The end result of all this is that doing as you want requires a fair number of changes to your system. This task is possible -- or at least, it was with Windows 7 and 8. (I have yet to hear any reports of people making such changes with Windows 10.) There are a few Web sites out there that go into all the gory details. One I know of is:


Note that I've not followed that precise set of instructions, but I did convert a Windows 7 system following another set of instructions, which have since been removed. I did this so long ago that I can't offer much in the way of specific advice, just point you to a set of instructions and hope that they work. I do want to make one more comment, though. You wrote:

I believe my PC will be better with CSM disabled

Why do you believe this? What do you hope to achieve? In most cases, the biggest advantage of EFI-mode booting is that it's a few seconds quicker -- but even this isn't always true. To be sure, there are other advantages to EFI-mode booting, but before you go mucking with your boot loader and partition table (which could easily lead you to lose everything on your disk if you make a mistake), you should evaluate your reasons for making this change so as to assess whether it's worth the risk. Even if it goes smoothly, you could easily put an hour or two into such a project, which will be hard to recover if you end up saving ten seconds in boot time once a day. If things go badly, you could put many hours into it and lose irreplaceable data. Really, this is a long-winded way of saying "if it ain't broke, don't fix it."

  • Thanks for your response, I had just been googling it and found this article social.technet.microsoft.com/wiki/contents/articles/… which seems to go through similar steps... To be honest, the 2 reasons I wanted to change is that the BIOS on my mobo sometimes goes a bit weird with CSM mode enabled and seems better without it, plus it's faster (and more secure?) the install is less than a week old and all data is replaceable... Also, I'm a sysadmin and don't mind breaking things to find out if they work. If this works I will update!
    – Rumbles
    Sep 13, 2015 at 19:25
  • Nice one, that worked, although I used the guide on the technet article rather than the link you sent I have marked as answered. Reading through both guides basically do the same thing more or less.
    – Rumbles
    Sep 13, 2015 at 21:44

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