UPSs and diesel generators are two backup systems which are kept by website hosting service providers in their data centers in the event there are interruptions in the main power source or the current is unsound and unable to support the appropriate running of the web servers based inside the facility. UPS is short for Uninterruptible Power Supply or Uninterruptible Power Source and it's a highly effective battery that works non-stop. It is connected to both the electric power network and the servers at all times, so when the power stops, the UPS is already up and running, 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 machines up and running for a longer period of time. If there is an outage, the UPS gives the required time for the diesel generator to start and then to take over until the primary source is restored.