(v.) To copy files to a second medium (a disk or tape) as a precaution in case the first medium fails. One of the cardinal rules in using computers is back up your files regularly. –webopedia
a backup or the process of backing up refers to making copies of data so that these additional copies may be used to restore the original after a data loss event –wikipedia
To create a copy of data as a precaution against the loss or damage of the original data. Most users backup some of their files, and many computer networks utilize automatic backup software to make regular copies of some or all of the data on the network. Some backup systems use digital audio tape (DAT) as a storage medium –KrollOnTrack
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