UPS is an abbreviation for Uninterruptible Power Supply or Uninterruptible Power Source. That is a battery which is used to power your personal computer or a server to prevent the loss of data when the main power supply fails for reasons unknown or becomes risky. A diesel generator basically self-explanatory. UPSs and generators are widely-used as a backup in data centers to back up the main power source and to ensure the consistent operation of all the machines located there. Because the UPS operates at all times, it provides the desired power for the web servers to remain functioning until the generator starts and takes over. Using this sort of a backup is vital for any data center or web hosting provider that wants to keep their hardware and info intact in case there is a power surge or outage, because it gives them enough time to react until the issue is resolved and the main power supply is restored.