UPSs and diesel generators are two backup systems that are kept by hosting providers within their data centers in case there are interruptions in the primary power source or the current is unsound and unable to support the proper functioning of the servers based in the facility. UPS stands for Uninterruptible Power Supply or Uninterruptible Power Source and it is an efficient battery which works non-stop. It's connected to both the power network and the servers constantly, so when the power stops, the UPS is already up and running, which helps prevent the servers from going down even for a second. The diesel generator is literally an engine which can give you the necessary power to keep the machines up and running for a longer period of time. In the event of an outage, the UPS provides the required time for the diesel generator to start and then to take over until the main source is restored.