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The word may be used as a noun, e.g., "have you remembered to move the backup to a safe place?", or as a verb, "he didn't back up the data, so we lost last week's work". Also common are various combinations, such as backup copy, backup software (the applications that are used for performing the backing up of data, i.e., the systematic generation of backup copies), backup policy (an organisation's procedures and rules for ensuring that adequate amounts and types of backups are made, including suitably frequent testing of the process for restoring the original (production) system from the backup copies).
As of 2004, backups are most often made from hard disk based production systems to large capacity magnetic tape storage, or optical disk WORM media like CD-R and DVD-R and similar formats. During the period 1975–95, most personal/home computer users associated backup mostly with copying floppy disks.There are four primary metrics relating to data backup:
Computer backups are useful primarily for two purposes, the first and most obvious is to restore a computer to an operational state following a disaster also called disaster recovery. This includes loss of a hard disc or the file system becoming so badly corrupted it cannot be read. The second use, often overlooked but probably more common, is to facilitate the recovery of a single file or set of files when they are accidentally deleted or corrupted by the user or a program.
Proper backup procedures require redundancy of the backup to a remote location and rotation schemes such as the GFS method ( Grandfather-Father-Son Backup). Storing the copy near the original is unwise, since many disasters such as fire, flood and electrical surges are likely to cause damage to the backup at the same time.
A backup is only as useful as its associated recovery strategy. Having a complete set of backup tapes is of no use if the only copy of the software required to read them is on one of the tapes. It is also possible for backup software to run successfully for several months, only to fail when it is needed most due to read errors on the backup media. Magnetic tapes in particular should be read-tested on a regular basis.
Computer terminology Computer storageThe terms storage ( U. or memory ( U. refer to the parts of a digital computer that retain physical state ( data) for some interval of time, possibly even after electrical power to the computer is turned off. The anthropomorphic term memory has been used