Software that copies data from a single machine or from selected computers in a network to a storage medium. At periodic intervals, a backup of the entire hard drive or of selected files and folders can be performed. Backup programs can also be set up to back up files automatically right after they have been updated and saved.When the Hard Disk CrashesCompany and personal data are the most valuable information to back up. However, if only data are backed up, the OS and applications have to be re-installed, which can be time consuming and costly, not to mention aggravating. The method often recommended is to back up the entire system, including OS and applications. After a disk crash, everything can be restored to the replacement hard drive, and users can resume from that backup point. See backup storage, backup types, backup server, HSM, data recovery and active archiving.