A backup is nothing more than an additional copy of data, ideally kept in a different location than the original.
If there’s only one copy of something – say a photograph on a mobile phone – then it’s not backed up. If that device were to fail or be lost, then the photograph would be lost forever as well.
Computers are excellent at making copies of digital data, and backups are one important use of that functionality.
It’s generally recommended that important data be backed up in at least one, ideally more, separate devices or media, such as an external hard disk. In addition, it’s recommended that critical data also be backed up in another physical location, such as a different building, or online.
More than anything, the important concept is that there never be only a single copy of important data. That’s not backed up.
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