Chapter 10 Install and System Administration for FortiOS 5.0 : Basic Administration : Configuration backups : Configuration revisions
  
Configuration revisions
The Revisions options on the System Information widget enables you to manage multiple versions of configuration files. Revision control requires either a configured central management server, or FortiGate units with 512 MB or more of memory. The central management server can either be a FortiManager unit or the FortiCloud.
When revision control is enabled on your unit, and configurations have been backed up, a list of saved revisions of those backed-up configurations appears.