Skip to contentGo to the directory tree
Windows Directory Tree
  1. C:
  2. Windows.old
FolderRisk: Caution

Windows.old C:\Windows.old

Previous Windows installation kept after an upgrade so you can roll back; removed automatically after 10 days.

Updated on By AltF4 Formation

What it’s for

Windows.old is the copy of the previous installation, created during an upgrade. It holds the files that let you go back to your earlier version of Windows.

What it contains

  • The Windows, Program Files, ProgramData and Users folders of the previous installation.
  • The folder is not hidden. It appears after an upgrade, or after a clean install on a volume that already contains Windows.
  • During the upgrade, Setup uses it as a staging area for files and settings moving to the new installation. Afterwards it keeps the old system files and any user files that were not migrated.

Risks and best practices

  • Windows removes the previous version automatically ten days after the upgrade. Deleting it sooner gives up the rollback, and nothing undoes that, so first check that the new version works.
  • To remove it cleanly, open Settings > System > Storage > Temporary files, select “Previous version of Windows” and remove the files. Administrator rights are required, and deleting from File Explorer fails on protected files.
  • Recover any data you need from Users before deleting.

Useful commands

Fenêtre de terminal
# Approximate size (can be slow)
$b = (Get-ChildItem C:\Windows.old -Recurse -Force -ErrorAction SilentlyContinue | Measure-Object Length -Sum).Sum
[math]::Round($b / 1GB, 1)
Fenêtre de terminal
:: How many days are left before automatic deletion?
DISM /Online /Get-OSUninstallWindow


:: Extend that period (2 to 60 days) while Windows.old still exists
DISM /Online /Set-OSUninstallWindow /Value:30


:: Open Disk Cleanup
cleanmgr

Report a mistake