Web archiving does not include the practice of backing up the code of web pages as they are created and updated, but it assumes that this backing up takes place. Preferably there should be two or more backup copies of the entire website as it is made and altered. The backups should not all be on the same computer; at least one should be on a portable harddrive, backup tape cartridge, network-accessible server, or set of CD-ROM disks, and these external locations should be sustained in accordance with archival best practices.