UPSs and diesel generators are two backup systems that are kept by website hosting providers inside their data centers in the event there are interruptions in the main power source or the current is shaky and unable to support the appropriate operation of the machines situated in the facility. UPS is short for Uninterruptible Power Supply or Uninterruptible Power Source and it is an efficient battery that works non-stop. It's connected to both the electric power network and the web servers consistently, so anytime 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 an engine that can deliver the required power to keep the servers functioning for a longer period of time. In the event of an outage, the UPS gives the necessary time for the diesel generator to start and then to take over until the main power source is restored.