Windows Operating System upgrades as well as version updates would leave plenty of files behind in the system drive. This is because Windows keeps the files from previous versions of Windows in a separate folder, in case the user wants to rollback the major update (or OS upgrade).
For instance, the Windows 10 Anniversary Update v1607 gives you 10 days before which you have the option to rollback to the previous build or version. After 10 days the option to go back wouldn’t be available as the respective folders are cleared automatically. If you’ve upgraded to Windows 10 from Windows 7 or 8, the previous Windows installation folder (Windows.old) is retained for 30 days.
After the stipulated time (days), the corresponding folders will be wiped out automatically by Windows. These are the folders that would be emptied:
Windows10Upgrade (this applies if you used the upgrade assistant tool)
If Windows doesn’t automatically clear those folders, you can use Disk Cleanup or Storage Settings to remove Windows.old and the other folders.
You can immediately free Up 20 GB+ disk space After Installing a Major Update or OS Upgrade, if you don’t plan to rollback the update.
Typically, the amount of disk space freed up might be anywhere between 14 GB to 25 GB depending upon the bitness of your Windows installation, and the number or programs installed in the system drive.
Clearing Windows.old Using Disk Cleanup
First, Disk Cleanup (cleanmgr.exe) doesn’t list Previous Windows installation if you’re not running it as administrator. To elevate it, click the option Clean up system files button in the Disk Cleanup window. Or simply run it as administrator from Start menu. To do so, click Start, type Disk Cleanup, and right-click Disk Cleanup from the results and choose Run as administrator.
In the next dialog that appears, select the following checkboxes if available:
- Previous Windows installation(s)
- Temporary Windows installation files
- Windows Upgrade log files
Click OK. You may uncheck the other items if you don’t want to clear them.
Disk cleanup would now warn you that if you clean up the previous Windows installations or temporary installation files, you will no longer be able to restore the machine back to the previous version of Windows. That’s a fair warning.
Click Yes, and let Disk Cleanup do its job.
If the Disk Cleanup utility doesn’t list the Previous Windows installation(s) entry, or it throws up an error when cleaning up, use Windows 10’s Storage Settings app to clean up previous versions of Windows folder.
Clearing Windows.old Using Storage Settings App
Click Start, type Storage and click Storage (System settings)
Click Temporary files, and this further drills down the items in the next window.
Under Previous version of Windows, click Delete previous versions. You won’t be asked for a confirmation.
Note: Previous version of Windows stuff occupies atleast 25 GB of space. In the above screenshot, it shows 3.22 GB because I’ve manually cleared stuff from the Windows.old folder prior to running the Storage settings app. So in your case, the space freed up will be much…much higher. In my test system where it showed 27 GB used by Previous version of Windows (upgraded from Windows 7 x64), it took around 7 minutes for the Storage settings app to assess and clear the Windows.OLD folder.
Delete Windows.old Manually
Deleting Windows.old using Disk Cleanup or Storage Settings sounds very easy, but they fail to clear the folder in some situations. If they don’t work in your case, you should be able to delete the Windows.old folder manually with the required folder permissions.
Right-click Start, click Command Prompt (Admin)
Type the following commands and press ENTER after each command:
TAKEOWN /F C:\Windows.old /R /D Y icacls C:\Windows.old /grant administrators:F /T
The above is to take ownership of Windows.old, its sub-directories and all the files within and assign full control Permissions for the Administrators group. So the process might take some time to complete.
Then, run the following command:
RD /S C:\Windows.old
That should remove Windows.old completely.
Now, the option to Go back to an earlier build should be dimmed out.
About the author
Ramesh Srinivasan founded Winhelponline.com back in 2005. He is passionate about Microsoft technologies and has a vast experience in the ITeS industry — delivering support for Microsoft's consumer products. He has been a Microsoft MVP [2003 to 2012] who contributes to various Windows support forums.