Windows.old is 20 to 40 GB and deletes itself in ten days
The folder left by a Windows upgrade, why it disappears on its own, and how to remove it early without breaking the way back.
After a feature update, Windows keeps the previous installation in C:\Windows.old. It is routinely 20 to 40 GB, it is the single largest thing on many machines for a week and a half, and Windows deletes it automatically after ten days without telling anybody.
What it is actually for
It is the way back. For those ten days, Settings, System, Recovery offers Go back, which restores the previous version of Windows using that folder. Remove it and the option disappears immediately, which is the entire trade.
When to keep it
- You have just upgraded and something is wrong. A driver, an application, anything that worked before. Keep it until you are sure.
- You upgraded across a major version. The chance of finding a problem in week two is higher.
- You have the space. If the drive is not full, there is no reason to hurry.
When to remove it
If the drive is full enough that it is causing problems, or the upgrade has clearly gone fine, it can go early. Removing it is not a disk operation you do by hand:
- Open Settings, System, Storage.
- Choose Temporary files.
- Tick Previous Windows installation(s).
- Remove files.
Disk Cleanup's Clean up system files button offers the same thing under the same name. Both are the supported route, and both correctly remove the recovery option along with the folder.
Why deleting it in Explorer fails
The folder is owned by TrustedInstaller and protected, so dragging it to the Recycle Bin produces a string of permission errors and, worse, can leave a partly deleted folder that still occupies space and can no longer be used to go back. Taking ownership to force it is the wrong answer to a problem Settings solves in four clicks.
If it is still there after ten days
That usually means the automatic cleanup has not had an idle window to run in, which happens on machines that are rarely left on and unattended. Removing it through Settings works regardless.
Once it is gone, the next places to look are in why the C drive is full, and the recovery side of the same question is System Restore and shadow copies.
Common questions
What is the Windows.old folder?
The previous Windows installation, kept after a feature update so the Go back option in Settings, System, Recovery can restore it. It is typically 20 to 40 GB and Windows deletes it automatically after ten days.
Is it safe to delete Windows.old?
Yes, once you are confident the upgrade went well. It removes the ability to go back to the previous version, which is the only thing it is for.
How do I delete Windows.old?
Settings, System, Storage, Temporary files, then tick Previous Windows installation(s). Disk Cleanup's Clean up system files offers the same option. Do not delete it in Explorer, where permissions will block it partway through.
Why can I not delete Windows.old normally?
Because it is owned by TrustedInstaller and protected. Deleting it by hand produces permission errors and can leave a partly removed folder that still uses space and can no longer restore anything.