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Windows Setup may leave the prior installation of Windows on your hard disk as a backup safety measure. I'll discuss and then delete it.

I am using Windows 7 and one time I had to reinstall it.

I reformatted the drive but it tells me that the drive can't be formatted because there is an operating system on the drive, so I re-install over the old OS but during the installation process, it informs me that the installation will backup the current OS in a folder called "windows.old"! I install correctly and everything works normally. I thought formatting was supposed to wipe the drive so a fresh install could happen, but windows won't let me delete the entire "windows.old" folder - apparently there is something in it that is system sensitive and off limits.

My question is, why does the new install create that "windows.old" folder and if it is safe to get rid of it(I understand it is!), how do I manage that?

A reinstall of Windows should allow you to reformat the drive. It may warn you that there's an operating system already on the drive - as it should - but ultimately you should still be able to indicate that you know what you're doing, and that the drive should be erased.

If you bypass that and install without the reformat - as apparently you have - Windows setup basically tries to be helpful by saving the prior installation.

Getting rid of it, if that's what you want, should be fairly easy.

I'm not sure exactly what steps you took or which messages you saw that would prevent you from actually formatting the hard drive and erasing everything on it as part of Windows setup. Yes, if you attempt to run the "Format" command from within Windows, that cannot work - you're asking Windows to erase the hard disk it's running from, and it simply cannot do that. Windows Setup, however, most certainly can when booted from the installation media.

"... before deleting anything you're uncertain of is to make a copy; back it up somewhere."

This article - What are the steps to upgrade Windows XP to Windows 7? shows the basic reformat and install steps for Windows 7. The important thing is to choose those options which cause Windows Setup to reformat the hard drive - erasing everything on it - prior to installing Windows.

If you don't use Windows Setup to reformat your hard drive, and you choose a "custom" installation, Windows Setup will save your previous Windows Installation in a folder named "windows.old". I'll be honest, and admit that I don't know exactly what is saved there. I've read that it can be used to restore your machine to the prior installation, but I've never used it. I very much prefer, and strongly recommend, using a system backup prior to the installation to preserve the entire prior state of the machine should you need to revert.

So, if I see it, I delete it, but first...

The fact that you can't delete it concerns me a little. To diagnose this I would:

  • Rename "Windows.old" to something else.

  • Reboot.

  • See what fails.

It's possible, I suppose, that you might need to reboot into safe mode to be able to rename the folder, but I'm thinking probably not.

If a file in use was preventing the folder from being deleted, having renamed it should cause whatever was using it to no longer be able to find it. You might now see an error related to that.

There's no way for me to know what might happen at this point. Depending on what fails you might now know to make a change of some sort, you might do nothing, or you might end up renaming the folder back. But you should have some more information on why you were unable to delete the folder in the first place.

Once that's understood, you can decide to delete the folder.

In your case, I don't know if you're appropriately backed up or not, so I'll fall back on my standard recommendation before deleting anything you're uncertain of is to make a copy; back it up somewhere. Copy the entire folder elsewhere, just in case. That way if you find out some time later that you really wanted it, you can restore it from this saved backup copy.

If you still get an error deleting the folder, make sure you are logged in as administrator, and are running a Windows Explorer instance as the administrator. In Windows 7, right click on the Windows Explorer icon in the task bar, right click on the Windows Explorer item in the resulting popup menu, and then click on Run as administrator.

Menu location of Run As Administrator in Windows 7

Alternately you can also fire up a Windows Command prompt using a similar sequence, and enter the following commands (highlighted in bold):

C:\Users\LeoN> CD \
C:\> RD /s Windows.old

BE CAREFUL: make sure that it's Windows.old you're deleting, and not Windows itself.

That could have you starting the whole installation over again, from scratch.

Article C4298 - May 6, 2010 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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10 Comments
Bob
May 6, 2010 5:18 PM

Leo,
Thank you for your quick reply and explanation.

My mistake was that I, like an idiot, was trying to reformat the C drive FROM the C drive, and naturally, I couldn't so it created the "windows.old" folder to protect itself!

However, unless I have missed something in your reply pointing the way, I don't understand how to format the OS drive from WITHIN Windows itself that would eliminate going through this loop.

I resolved the question by simply re-installing the OS anyway and then using disk cleanup after the fact and it simply eliminated the folder - indicating Windows found no vital files in that backup folder that would make the new installation unstable if eliminated.

Problem solved - I love Windows 7

You cannot format the C: drive (the drive Windows is installed on) while Windows is running.
Leo
07-May-2010

Mark
May 7, 2010 3:11 AM

Whenever I reinstall I leave windows.old for a week just in case there is anything I may have missed when I backed up. I've never need it because all I needed was on the backup, but if you didn't back up there are a few things you can manually recover from windows.old such ad t-bird account settings, address book and emails. Browser shortcuts and saved passwords etc. I've used may backups to get these back but I'm on of the paranoid (It's not really paranoia there really are bots out there after your data, not to mention my own mistakes and natural disasters) ones who backs up my backups. On my first programming job the boss was required to have one of the 3 backup disks at home home and that copy could never be more than 3 days old.

Dave Markley
May 11, 2010 9:34 AM

Windows.old is simply a backup of what's currently on your hard drive at the time when Windows 7 installs, but don't rely on it to save everything, mistakes do happen. What I've done in the past and highly recommend is create a partition using most of your current 'free space' and install Windows 7 there. By default this new (with Windows 7) partition should become Drive 'C', then you can delete your original partition once you're sure you've retrieved any files you may want. (Also, you can 'drag and drop' any files you want from the 'old' drive to the new 'C' drive this way). Just a suggestion, but I always use 'Treesize Free' to go through the old drive to make sure I've recovered anything I may want.

robert p
May 11, 2010 10:28 AM

One step noted above was to rename the folder and see if that causes later problems. This is a very neat and effective method for making certain one can safely delete a file/folder. I have explained this to my clients who have many computers and they want to know if something is safe to delete. There is no uninstall, so I have them rename the file or folder, usually just adding an "_x" to the end. Then operate for a while to see if anything bad happens or they get error msgs. If not, probably safe to delete.

Dennis D
May 12, 2010 8:50 AM

Windows.Old can be deleted by right clicking the drive it's on, probably C:, click on Disk Cleanup then click on Clean System Files.

That should do the trick.

Andy
May 13, 2010 1:48 AM

I personally like the notion of windows.old simply because it provides that extra measure of assurance that something might be there that I missed during my pre-installation back up. On both occasions when I upgraded to Win 7, I managed to review the .old folders and delete both without a problem...simply right click and delete. I remember reading Microsoft literature stating that this was doable, so I did this successfully.

Andy
May 13, 2010 1:54 AM

Further to the above, the windows.old folder saved me time from reloading personal files (music, photos, movies, docs) from the old OS to the new one. I didn't think these files needed to be removed completely in particular for them to work any better on the new OS via back-up.

Frank D
January 13, 2012 10:56 AM

I have recently upgraded from Vista to Win 7 and want to delete old windows files. How do I determine what files are in the old windows OS and what are not so that I don't delete the files that I want. Thank you.

Gabby
February 5, 2012 6:52 PM

Well, I have the computer backed up and everything and I'm pretty sure Windows.old isn't running anything, if it is it is unseen but the computer fails to delete the folder on the cmd prompt saying if I was sure, and after saying yes or Y to the cmd prompt it said that the folder was not found and I could see it in the c: drive... am I doing something wrong?

Mark J
February 6, 2012 2:19 AM

@Gabby
Unlocker Assistant often helps in situations like that.

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