Files with the .BCK extension contain backups of files or entire volumes of files in the VMS VAX or VMS Alpha operating systems for business-class servers from the eighties and nineties of the twentieth century. BCK files were created to protect important data from loss or damage.

VMS systems, developed by Digital Equipment, were used to manage enterprise servers. The BACKUP tool was used to archive data in the form of recordings on disks or magnetic tapes. The VAX-11/VMS and VAX/VMS systems have been replaced by OpenVMS.