The terms Recovery disc (or Disk), Rescue Disk/Disc and Emergency Disk[1] all refer to a capability to boot from an external device, possibly a thumb drive, that includes a self-running operating system: the ability to be a boot disk/Disc that runs independent of an internal hard drive that may be failing, or for some other reason is not the operating system to be run.[2]
The focus of recovery or rescue is not to lose the data files on the hard drive; the focus of restore is to restore the operating system's functionality (and subsequently restore the contents of one's latest backups).[3]
The rescue/recovery tool uses media containing a backup of the original factory condition or a favored condition of a computer as configured by an OEM (original equipment manufacturer) or an end-user. OEM supplied media are often restore tools shipped with computers to allow the user to reformat the hard drive and reinstall the operating system and pre-installed software as it was when it was shipped.[4] Many modern systems have eliminated use of a physical recovery disc and instead store this software in a separate partition on the hard disk itself.