If you install Windows 11 on a computer that has Windows 10 installed or if you perform a custom installation of Windows 11 instead of an upgrade installation, you will see a Windows.old folder on your system drive. Similarly, even if you install Windows 11 or Windows 10 by performing a custom installation and don’t format the partition during the installation process, files that were used in your previous version of Windows are stored in the Windows.old folder. In short, whenever you upgrade your Windows to a later version, you will see a new folder called Windows.old created on your disk.

Windows.old folder in Windows 11/10

The Windows.old folder is generated if the following conditions are true:

You install a newer version of Windows on a computer on which an earlier version of Microsoft Windows is installed.
You perform a custom installation of Windows Vista, Windows 7, Windows 8, Windows 10, Windows 11 instead of an upgrade installation.
You install Windows Vista, Windows 7, Windows 8, Windows 10, Windows 11 on the drive on which had an earlier version installed.

This Windows.old folder contains the following folders from your old Windows installation:

Windows
Documents and Settings
Program Files

You can use this folder to retrieve any documents from your old installation, as follows:

Click Start, type %systemdrive%\Windows.old in the Start Search box, and hit Enter.
Retrieve the files from the Windows.old folder.

Alternatively, you may simply use the Recover Personal Files Tool to retrieve files from the Windows.old folder.

Delete or remove Windows.old folder

After a Windows Upgrade, by default, a scheduled task is created and will run after four weeks to delete the Windows.old directory. But if you wish, you can also remove the Windows.old folder manually earlier. If you find that you no longer have any use for it, you may safely go ahead and delete it as follows:

Delete Windows.old folder using Disk Cleanup

Open Disk Cleanup Tool and select Files from all users on this computer. Click the Disk Cleanup tab, and then look for the Previous Windows installation(s) check box. You will need to click on Clean up system files button, in order to see this window.

Select Previous Windows installations. Click OK. This will remove the Windows.old folder.

Remove Windows.old folder using Command Prompt

Alternatively, you can also use a command prompt to delete files and folders from an earlier installation of Windows. To do this, Run ‘Command Prompt’ as administrator.

First, you will need to take ownership of this folder, so at the command prompt, type

takeown /F C:\Windows.old\* /R /A

and hit Enter.

Next, in the command prompt, type

cacls C:\Windows.old\*.* /T /grant administrators:F

and hit Enter. When you run this command, administrators are granted full rights to all files and to all folders.

Finally, type

rmdir /S /Q C:\Windows.old\

and hit Enter. This will delete the windows.old folder.

UPDATE: SpaceWalker189 says in the Comments below, you can create a BAT file as follows:

takeown /F C:\Windows.old\* /R /A
pause
cacls C:\Windows.old\*.* /T /grant administrators:F
pause
rmdir /S /Q C:\Windows.old\
pause

Copy-paste this in Notepad and save it as a .bat file.

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