Why Is Computer Backup Important, and How Is It Accomplished? A backup duplicates a file or program to protect an enterprise if the original is lost or damaged. A full, or archival, backup copies all of the programs and files in a computer. A differential backup copies only fi les that have changed since the last full backup. An incremental backup copies only files that have changed since the last full or incremental backup. A selective, or partial, backup allows users to back up specifi c files. Continuous data protection (CDP), or continuous backup, is a backup plan in which data is backed up whenever a change is made. Backup procedures specify a regular plan of copying and storing data and program files.