Dell XPS 15Z (L511Z, Mid 2011) - Manual (Page 65)

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You can restore the operating system on your computer using any of the following options:
CAUTION: Using Dell Factory Image Restore or the Operating System disc to restore
your operating system permanently deletes all data files on your computer. If possible,
backup your data files before using these options.
Option Use
System Restore as the first solution
Dell DataSafe Local Backup when System Restore does not resolve your problem
System recovery media when operating system failure prevents the use of
System Restore and DataSafe Local Backup
when installing the Dell factory‑installed software on a
newly installed hard drive
Dell Factory Image Restore to restore your computer to the operating state it was in
when you received your computer
Operating System disc to reinstall only the operating system on your computer
NOTE: The Operating System disc may not ship with your computer.
Restoring Your Operating System