UPSs and diesel generators are two backup systems that are kept by web hosting companies in their data centers in the event that there are interruptions in the primary power supply or the current is unstable and unable to maintain the correct functioning of the machines situated inside the facility. UPS stands for Uninterruptible Power Supply or Uninterruptible Power Source and it's an effective battery that works non-stop. It is connected to both the power network and the web servers constantly, so anytime the power stops, the UPS is already operational, which prevents the machines from going down even for a second. The diesel generator is definitely an engine that can deliver the needed power to keep the web servers working for a longer period of time. In the event of an outage, the UPS gives the needed time for the diesel generator to start and then to take over until the primary source is restored.