How to turn Windows 10 partition into system partition and delete old system partition?

Question

I have a hard disk containing the following partitions:

1. A 500 MB system reserved partition.
2. A 48 GB NTFS system partition containing an old, broken Windows 10 installation.
3. Some unused Linux partitions that we can ignore.
4. An active 77 GB NTFS partition containing my current Windows 10.

What I want to achieve: Delete the 48 GB partition and still be able to boot Windows on the 77 GB partition.

It's worth noting that the Windows installation on the 48 GB partition is broken and cannot boot. That's OK.

But the 77 GB partition still needs the other partition; otherwise it can't boot. I tried to do this:

1. Delete the 48 GB partition (using GParted in Linux).
2. Tried to boot the Windows that's on the 77 GB partition (via GRUB).
3. Windows failed to boot.
4. Booted from a Windows install disk and tried to repair Windows, but with no luck. The wizard couldn't find a fix.
5. Restored the deleted partition (using Testdisk in Linux as described in this video).
6. Tried to boot the Windows that's on the 77 GB partition (via GRUB).
7. Now Windows boots successfully again.

So we've established that my Windows needs that system partition. I want to get rid of it.

My living Windows partition (77 GB) is mounted as C:. The 48 GB partition is mounted as D:. I've tried to copy boot files using bcdboot like this (as described here):

bcdboot D:\Windows C:

... but this seems to do nothing. No matter what parameters I give bcdboot, it just prints out its usage instructions.

Am I using bcdboot wrong?

I do not have BitLocker or any other encryption on this disk. I believe my firmware uses BIOS rather than EFI (my motherboard is from 2010 or 2011).

Answer 1

It would be necessary to have more information than you've included in your question, and also I think you have multiple issues in combination.

However, I think your main question is how to get Windows to continue to boot when you have reclaimed the 48 GB from the broken Windows installation. And I believe I can help you with that.

The problem at present is that as you've found, if you remove the 48 GB partition, Windows will not boot. This is actually for two reasons: firstly, as you suspect, it may be your current System partition. Secondly though, Windows identifies boot volumes by partition index, so if you remove a partition, Windows will no longer find the partitions above it, as their partition indexes will have changed.

Armed with this knowledge, one thing you can do is to retain a tiny partition in the same location. This will resolve the incorrect partition indexing, although if your current Windows boot volume relies on that partition as its System partition, you will be out of luck and still unable to boot.

In that case (or just anyway), your solution is simply to delete all files* on the 48 GB partition and then reduce its size as much as possible in Disk Management. That way, you will preserve it as a System partition without having to take up any significant space such as a Windows installation requires.

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*Or, if in doubt, just delete all non-boot files. For example, the c:\boot folder may or may not be in use by your new Windows installation, as Windows can use hidden boot files instead. See this question for some pointers, but if you're not sure how it is on your system, retain any boot files—they are not large. You can certainly get rid of the huge old paging/hiber files. In your case you have already restored the partition previously, so worst case is if you delete something needed, just restore and try again more selectively.

Answer 2

Based on the general information you've provided, this should unstick the steps you began so that you can create a new system partition.

Please remember that Windows 10 was first released in 2015, and the 2012 article you are following is for Windows XP, Windows 2000 and Windows 7. Since that time there have been significant changes in Windows partition management: UEFI is now commonly used by Windows installations, along with a new EFI boot mechanism, and we now also have GUID partition tables, which give more flexible partition management (including removing the MBR limit of 4 primary partitions) and bring their own new boot possibilities. In general it's now considered preferable to use a GUID partition table (GPT) and UEFI boot, where your hardware and BIOS support these. If you want to explore that area further, this might be a good starting point, but there is plenty out there if you search for these terms.

Disclaimers aside, and assuming you stick with your current approach at least for now, the first thing to note is that your screenshot shows that your current system partition is not an EFI system partition. This makes it likely that the steps in the article will work for your machine. An EFI system partition shows up in Disk Management like this:

I believe you just need to make one correction to your bcdboot command in order to carry on and complete what you started.

The example in your linked page uses the following command:

Bcdboot D:\Windows /s S:

whereas you are using

bcdboot D:\Windows C:

For this to work, you just need to include the /s parameter, to designate the target system partition where boot environment files are copied:

bcdboot D:\Windows /s C:

This should allow bcdboot to continue as expected, rather than displaying usage info as it did when you tried.

I hope this enables you to complete the steps in the article you're following. At this point however, I do need to repeat my disclaimer about the article being from 2012, three years prior to the release of Windows 10.