When a feature update installs, Windows saves the entire previous OS version in a folder called Windows.old (located at C:\Windows.old ). This contains system files, drivers, apps, and settings.
Windows automatically creates a backup of the previous component state before applying a cumulative update. This uses Windows Component Servicing (CBS) and the Servicing Stack . windows 10 rollback update
This rollback system provides a safety net for both consumers and IT admins, making Windows 10 one of the most recoverable desktop OSes for update-related failures. When a feature update installs, Windows saves the