UPSs and diesel generators are two backup systems that are kept by web hosting companies within their data centers in the event that there are interruptions in the primary power source or the current is shaky and unable to maintain the appropriate running of the servers based within the facility. UPS stands for Uninterruptible Power Supply or Uninterruptible Power Source and it's a powerful battery which works non-stop. It's connected to both the power network and the web servers constantly, so anytime the power stops, the UPS is already operational, which helps prevent the web servers from going down even for a second. The diesel generator is an engine which can provide the needed energy to keep the web servers working for a longer period of time. In case of 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.