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 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.

See also: back up

backup (Wikipedia)

In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "back up", whereas the noun and adjective form is "backup". Backups can be used to recover data after its loss from data deletion or corruption, or to recover data from an earlier time. Backups provide a simple form of disaster recovery; however not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server.

A backup system contains at least one copy of all data considered worth saving. The data storage requirements can be large. An information repository model may be used to provide structure to this storage. There are different types of data storage devices used for copying backups of data that is already in secondary storage onto archive files. There are also different ways these devices can be arranged to provide geographic dispersion, data security, and portability.

Data is selected, extracted, and manipulated for storage. The process can include methods for dealing with live data, including open files, as well as compression, encryption, and de-duplication. Additional techniques apply to enterprise client-server backup. Backup schemes may include dry runs that validate the reliability of the data being backed up. There are limitations and human factors involved in any backup scheme.

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