Dual Boot - Delete a OS

How to Properly Delete a OS in a Dual Boot​

   Information

Deleting a double booted OS may seem simple - you just delete the partition with the OS you want to get rid of and you are done. Well, it is not that easy. With said approach you may get yourself into a lot of trouble. This tutorial describes a safe way how to properly delete a double booted OS.

Step 1 - Check where the bootmgr resides
Open Disk Management and find the partition that is marked "active". That is the partition that contains the bootmgr. If there are several active partitions, you have to look for the system flag - best seen in Computer.

The active partition is usually from the OS that was on the system first - e.g. if you installed Windows 7 on an XP system, the XP system would be the active partition. But there are also other cases.

If Windows 7 was the first OS on the system, then your bootmgr resides most likely in a separate system partition which is usually small.

If you installed Windows 7 as first OS to a disk that was not attached to the Sata port0, it can very well be that the bootmgr resides on an arbitrary partition on the disk that is attached to port0.

If you have e.g. a Dell system, your bootmgr may be on the recovery partition. Other OEMs may do the same, but I was not able to verify that.

This is the example of my current system. Note the two last partitions which are Windows 7 and Windows 8. The Windows 7 partition is marked as active. You also see that I have no small system partition because I have eliminated that partition after I moved the bootmgr from that small system partition to the Windows 7 partition.




If I would delete the Windows 7 partition, my Windows 8 would not boot any more because it would have lost it's bootmgr that is in cohabitation with the Windows7 bootmgr.

In order to avoid such an unfortunate situation, we launch the system that we want to retain and move the bootmgr to that system's OS partition. Here is how.
Step 2 - Delete the unwanted OS partition and reuse the space (Optional)
Stay in the OS that you want to keep and open Disk Management. Right click on the partition that contains the OS you want to delete and Delete Volume. Then right click on the deleted volume and Delete Partition. Now you should have "Freespace" where this partition originally was.

With Disk Management, you can define a new partition in that freespace or you can add it to the partition that shows to the left of that freespce. Just click on the partition which is to the left and Extend Volume.

If, however, you want to add that freespace to a partition that is to the right of the freespace, then you have to use an external tool. I suggest the bootable CD of Partition Wizard. Here is how.

A word of caution: before you manipulate partitions with Partition Wizard, make an image of all partitions on that disk. I once lost all my partitions on a disk because I made a small mistake manipulating one partition with Partition Wizard. For imaging I recommend Free Macrium. Here is how.
Step 3 - Cleanup the bootmgr
Now that we removed one OS, we have a surplus entry in the bootmgr. We will remove this entry with EasyBCD. As you can see in the picture, the operation takes only 4 clicks.

EasyBCD is a very handy tool for a variety of operations on the bootmgr. You should have that in your toolkit anyhow.






If you stop at this step, the MBR is still in a double boot configuration and when you boot, the BIOS will present you the black screen where you have to choose the operating sytem - although only one operating system is present. This is not a disaster, but it is an unnecessary step that requires your intervention.

The next two steps will reset the MBR to your current OS and then your system will automatically boot into that.

Important: You absolutely have to execute both Steps 4 and Step 5. If you only do Step 4, your system will not boot any more.

Step 4 - Clean the MBR




Step 5 - Reset MBR with the entry of the current OS

Related Tutorials

---

• How to Delete "Windows 8 Developer Preview" in your Dual Boot with Windows 7
• How to Setup a Dual Boot Installation with Windows 7 and Vista
• How to Do a Dual Boot Installation with Windows 7 and Windows 8
• How to Setup a Dual Boot Installation with Windows 7 and XP
• How to Setup a Dual Boot Installation with Windows Vista and XP
• How to Dual Boot Windows 7 and Ubuntu
• How to Delete an Operating System Listed in Windows Boot Manager
• How to Change the OS Name in Windows Boot Manager
• How to Recover a Partition Used by an Older OS in a Dual Boot

 

[SIW2]

You do such friendly tutorials.

 

[whs]

I am a friendly person.

 

[netbox]

Thanks for this easy to follow tutorial but Im a bit confused with this;

If Windows 7 was the first OS on the system, then your bootmgr resides most likely in a separate system partition which is usually small.

I want to install XP on another new partition on my Windows 7 HP laptop, Id check the disk management and the boot was in C:



so, if I delete XP I'll just delete the new partition where XP was installed and remove the boot menu entry via EasyBCD? is that okay?

 

[whs]

1. The OS into which you boot will always assume C for the OS partition, regartdles which OS it is.

2. If you install XP, the XP bootmgr will land in the 100MB active partition where the Win7 bootmgr already is.

3. Yes, the day you want to remove XP, you delete the XP volume and partition and cleanup the bootmgr with EasyBCD.

 

[boyans]

If I would delete the Windows 7 partition, my Windows 8 would not boot any more because it would have lost it's bootmgr that is in cohabitation with the Windows7 bootmgr.

Just a small note:

There is no Windows 7 boot manager and Windows 8 boot manager "cohabitation" !

If you can boot Windows 8 then ONLY Windows 8 boot manager is present on active partition. Windows 7 boot manager was replaced by Windows 8 boot manager during Windows 8 installation. (The file name for both is bootmgr and the file can be found on active partition in root folder).

Always the latest boot manager is in control of the booting in a dual or multi boot system based on Vista and later Windows versions.
Every Windows boot manager can boot earlier Windows systems - the oposite is not possible.

 

[GoofyGoober442]

Delete Non Active OS from Dual Boot

Hello

Currently I have Windows 7 Ultimate 32bit and 64 bit in a dual boot configuration. I installed the 32bit version first therefore under disk management it is marked as the active OS.

I want to delete the 32 bit version and keep the 64 bit version of Windows 7. I am very leery of errors and want to avoid the "BOOTMGR IS MISSING CTRL-ALT-DELETE TO RESET".

My question is.... Can I delete the 64 bit OS which is not marked as active, then boot into my 32 bit OS and install Windows 7 64 bit over the 32bit so that I end up with just Windows 7 64 bit as my main OS?

To install the Windows 64 bit over the 32 bit version I would just install the 64 bit version and then run windows cleanup to erase the 32 bit version. This way I would not have to format the partition with win7 32 bit and therefore reduce my chances of getting the BOOTMGR error described above.

Sorry if this is difficult to understand but I tried...

Here is a screen shot of my disk management for reference.
PS: I was logged into the 64bit partition when I took the screen shot.

If any of you could please help me out or give insightful advice as to what I should or should not do please let me know.

Thanks!

 

[whs]

Unless you have another reason to reinstall the 64bit version, I would move the bootmgr to the current 64bit version (which I believe is C right now as per your picture). Then you can get rid of the 32bit version. http://www.sevenforums.com/tutorials/209885-bootmgr-move-c-easybcd.html

 

[mz7thc]

Windows 8 does not boot without old Windows 7

Hi there,
I moved the BCD to the Windows 8 drive. I have now two active drives, the one with Windows 8 on it is the boot disk and one with Windows 7.


If I disable the Windows 7 drive in Bios, I get a disk read error when booting up. I am also unable to delete the old drive.
I am a bit stuck here and don't know how to (safely) proceed.

Hope someone can help, thanks.

 

[whs]

It is apparently looking for the bootmgr on the Win7 disk. How did you 'move' the BCD?

 

[LittleJay]

Thanks for another good tutorial WHS! EasyBCD is most definitely a handle tool to have on hand.

 

[whs]

You are welcome

 

[mz7thc]

I used EasyBCD as described in step 1

 

[mz7thc]

Just noticed when I unplug a disk which is not related to Windows (e.g. MyDocuments), Bios is still pointing to the right boot disk, I get also an read error and Windows does not start. That means if I have to change my disks at some stage, Windows won't boot anymore...

 

[whs]

Just noticed when I unplug a disk which is not related to Windows (e.g. MyDocuments), Bios is still pointing to the right boot disk, I get also an read error and Windows does not start. That means if I have to change my disks at some stage, Windows won't boot anymore...

It is possible that the bootmgr is on the wrong disk. Post a full picture of your Disk Management and we'll have a look.

 

[mz7thc]

That's an interesting thought! How can I find out where the bootmgr is located?

 

[whs]

I think you are OK in this regard. The bootmgr is on C (active partition). D is also an active partition, but the current bootmgr is most likely not there.

 

[mz7thc]

How can I check this?

 

[thunderwolf333]

can someone help me, I did step 4 but when I try step 5 the program hangs and says not responding. now I dont have windows 7 listed to boot so I can't restart!

 

[whs]

That is worst case. Apparently your system was failing.

Try to rebuild the MBR with the bootable CD of Partition Wizard (last entry on the webpage). Burn this .iso to CD (e.g. with ImgBurn) and boot the system with the CD.