UPSs and diesel generators are two backup systems that are kept by web hosting service providers inside their data centers in case there are interruptions in the main power supply or the current is unsound and unable to maintain the appropriate operation of the servers situated within the facility. UPS is short for Uninterruptible Power Supply or Uninterruptible Power Source and it is a highly effective battery which works non-stop. It's connected to both the electric power network and the servers consistently, so when the power stops, the UPS is already operational, which prevents the servers from going down even for a second. The diesel generator is definitely an engine which can provide the required energy to keep the servers functioning for a longer period of time. In case of an outage, the UPS gives the necessary time for the diesel generator to start and then to take over until the main power supply is restored.