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Backup refers to the process of making copies of data or data files to use in the event the original data or data files are lost or destroyed. Secondarily, a backup may refer to making copies for historical purposes, such as for longitudinal studies, statistics or for historical records or to meet the requirements of a data retention policy. Many applications, especially in a Windows environment, produce backup files using the .BAK file extension.
Not all backup systems or backup applications are capable of completely restoring a computer system or other complex system configurations such as a database server, computer cluster or active directory servers. Managing the backup process involves organization and is a complicated process. An unstructured backup may simply consist of a stack of floppy disks, CDs or DVDs. However, it is obvious that security and ease of data recovery are both severely compromised.
Full and Incremental Backups: These begin with all data being backed up. Then, only new or modified data or data files are backed up, a much smaller segment of all data. Restoring the entire system to the data state at a specific point in time would require the last full system backup plus all the incremental backups done up to that point in time.
Differential Backup: This copies all data and data files that have changed since the last full backup. However, there is no archive attribute or record, meaning there is no record of when the backup occurred or how the data was changed.
Full System Backup: This allows the computer system to be restored as it was at a given point in time, including the operating system, all applications and all data. It makes a complete image of the computer, then the user may reconstruct any data changes after that point in time, possibly with an incremental backup.