Barratt is the author of BackupPC, an open source backup system. Costs and payback period are shorter if no complementary/backup system is required. The Exec and the file backup system are fully integrated. Bup is a Backup system written in Python. The site had not established an external backup system. Fault-tolerance is gained, but the identical backup system doubles the costs. Box Backup is an open-source, completely automatic online backup system. A backup system contains at least one copy of all data considered worth saving. The aircraft's guidance is pre-programmed, but a radio-control backup system is provided. BackupPC is not a block-level backup system like Ghost4Linux but performs file-based backup and restore. To prevent data loss, DynamoDB features a two-tier backup system of replication and long-term storage.