UPSs and diesel generators are two backup systems that are kept by hosting service providers within their data centers in case there are interruptions in the primary power source or the current is unsound and unable to maintain the correct running of the servers located in the facility. UPS is short for Uninterruptible Power Supply or Uninterruptible Power Source and it is an effective battery which works non-stop. It's connected to both the electrical power network and the web servers at all times, so if the power stops, the UPS is already functioning, which helps prevent the machines from going down even for a second. The diesel generator is an engine that can deliver the needed electric power to keep the machines working for a longer period of time. In case there is an outage, the UPS provides the required time for the diesel generator to start and then to take over until the main power source is restored.