UPS is an abbreviation for Uninterruptible Power Supply or Uninterruptible Power Source. It is a battery which is used to power a computer or a web server to prevent the loss of information in case the main source of energy fails for some reason or becomes unstable. 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 continuous functioning of all the web servers located there. As the UPS runs at all times, it provides the required power for the machines to remain operational until the generator starts and takes over. Using this kind of a backup is critical for any data center or service provider that wants to keep their hardware and info intact in case of a power surge or outage, since it offers them lots of time to react until the problem is resolved and the main power supply is restored.