UPSs and diesel generators are two backup systems that are kept by hosting companies in their data centers in the event there are interruptions in the primary power supply or the current is unstable and unable to sustain the correct functioning of the servers located in the facility. UPS refers to Uninterruptible Power Supply or Uninterruptible Power Source and it's a powerful battery which 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 working, which prevents the servers from going down even for a second. The diesel generator is certainly an engine which can deliver the necessary power to keep the web servers functioning 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 supply is restored.