The Duplicate

Whether you call it a clone, a bootable backup, a mirror, or a carbon copy, a duplicate is a complete, exact copy of your entire hard disk that (if it's stored on, or restored onto, a hard disk) you can use to start up your computer if necessary. Duplicates are wonderful because they enable you to get back up and running extremely quickly—in most cases, with only minutes of down time.

Consider this typical scenario: you've duplicated your Mac's internal hard disk onto a FireWire drive. One day your computer won't start at all; the screen displays a blinking question mark indicating that it can't find a valid system. You suspect a catastrophic hard disk crash. No problem: you quickly hook up your backup drive and boot from that. Your ...

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