UPSs and diesel generators are 2 backup systems that are kept by website hosting companies within their data centers in the event there are interruptions in the primary power supply or the current is unsound and unable to sustain the proper functioning of the servers based inside the facility. UPS is short for Uninterruptible Power Supply or Uninterruptible Power Source and it's a powerful battery that 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 definitely an engine that can give you the needed energy to keep the servers up and running for a longer period of time. In the case of an outage, the UPS gives the necessary time for the diesel generator to start and then to take over until the main source is restored.