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I've recently upgraded from Windows 7 / VMware to Windows8 / Hyper-V with my Dell M6600 and I'm really please with the result.

I admit though I like to run the latest stuff so I was wondering is there a way to convert the boot disk from BIOS / MBR to UEFI / GPT without doing a clean install.

I also have a second drive in the laptop; does this need converting too ?

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up vote 4 down vote accepted

@Ramhound: Mac OS X only requires a GPT partitioning scheme to INSTALL, it will boot from MBR if your copy the OS to such a disk.

@John: The simple answer is no, you can't. Here's why.

You should not convert a Windows installation in place, you should instead install from scratch. This is one of those problems where you would spend more time making copies of your data, and technical massages of the machine to get it to do what you want than simply reinstalling.

Windows does not care about not boot disks, so you can make your secondary disk into a GPT disk if you want to. You would have to do this if you had a 3TB drive anyway. Now, there are no easy tools to convert in place, you would be wiping the drive clean to change to GPT. (Remember, GPT and MBR are the underlying structure of the partitioning scheme, so by changing them, you are wiping the partition table clean.

Now, you were not clear on your usage of Hyper-V, is your system installed on top of Hyper-v? If so, then the answers change, because your system can be "copied", reinstall Hyper-V onto the GPT disk, then "copy" the system back, and you don't go through the reinstall process.

This is not how most people use there computer, but you mentioning these system makes this a possibility.

Sorry I can't be more positive.

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Thanks for the feedback; your correct; I keep the host operating system as 'clean' as I can get away from it and spend most of my time on Virtual Machines running in Hyper-V so it's not a big pain for me to copy them into my NAS reinstall the host and bring them back over. – John Kattenhorn Sep 25 '12 at 9:12
As a note, GPT fdisk can convert MBR<->GPT without touching the partitions' data – Teo Klestrup Röijezon Jan 7 '13 at 21:47
It's presumptuous to claim that you can't convert from MBR to GPT without data loss. Check gptgen. – Milind R Feb 3 '14 at 13:40

is there a way to convert the boot disk from BIOS / MBR to UEFI / GPT without doing a clean install.

Yes, apparently, by means of utilizing a 3rd party tool called "GPTgen".

See the tutorial here (Nope, it's not mine)

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I've used it, and yes, it works. Well. Flawlessly in fact. – Milind R Feb 3 '14 at 13:40

If your motherboard does not support UEFI and uses a legacy BIOS instead, it cannot be upgraded.

You can however likely still use a GPT partition table as it contains a legacy MBR for old BIOS systems.

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BIOS systems usually do not need a MBR (or any partition table, for that matter). It's only Windows that refuses to boot from GPT-only disks in BIOS mode. – grawity Sep 14 '12 at 10:08
@grawity - Mac OS X also requires a UEFI BIOS to boot to a GPT parition. It also is important to note that Solaris 10 doesn't support GPT at all. Its important to note this is the only correct answer for this question. Windows must be x64 to boot from a GPT and the computer must have a UEFI BIOS. Furthermore MBR is booted first if its a hybrid system. – Ramhound Sep 14 '12 at 11:03
@Ramhound: Either way, it's an OS bug, not requirement by the BIOS. Also, if a computer lacks UEFI firmware (not "UEFI BIOS"), it is possible to install UEFI DUET to disk, though it's too much work for anything else than development. – grawity Sep 14 '12 at 11:21
The Dell M6600 supports both legacy BIOS and UEFI, it's currently using the BIOS option but I'm thinking as part of the upgrade process I would be switching it to UEFI. – John Kattenhorn Sep 14 '12 at 12:06

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