A storage device used to hold copies of data for backup and recovery. In large enterprises, magnetic tape libraries and magnetic disks are used for backup (see tape library and D2D). Optical technologies have also been used (see magneto-optic disk and WORM).Consumer StorageFor consumers, USB drives and external magnetic disk drives are common backup devices. Write-once and rewritable optical media such as CDs and DVDs were popular at the turn of the century, but their usage has diminished. Also infrequently used are Zip disks and other removable disks that came out in the same time frame (see magnetic disk). In the 1980s, the early days of personal computers, backup was not a priority among users; however, magnetic tapes were occasionally used (see QIC). See LAN-free backup.Backup LocationsMyriad backup services on the Internet are available for both enterprises and consumers (see cloud storage).The most secure local backup is on a removable medium, such as a USB drive, an external hard drive or on a drive in another computer. Backup files are also maintained on a second internal drive in the same computer, and sometimes, even on the same drive in a different folder, the latter providing the weakest protection. See backup types.