UPSs and diesel generators are two backup systems that are kept by website hosting service providers in their data centers in the event there are interruptions in the primary power supply or the current is shaky and unable to maintain the correct running of the machines based inside the facility. UPS is short for Uninterruptible Power Supply or Uninterruptible Power Source and it is a powerful battery which works non-stop. It is connected to both the electric power network and the servers all of the time, so if the power stops, the UPS is already operational, which prevents the machines from going down even for a second. The diesel generator is an engine which can give you the required power to keep the servers operational for a longer period of time. In the event of an outage, the UPS provides the necessary time for the diesel generator to start and then to take over until the primary source is restored.