UPS is an abbreviation for Uninterruptible Power Supply or Uninterruptible Power Source. It's a battery that is used to power some type of computer or a web server in order to avoid the loss of information if the main source of energy fails for some reason or becomes unstable. A diesel generator is more or less self-explanatory. UPSs and generators are used as a backup in data centers to back up the power and to guarantee the continuous running of all of the web servers located there. Due to the fact that the UPS runs at all times, it provides the necessary power for the web servers to remain functioning until the generator starts and takes over. Using this type of a backup is critical for any data center or web hosting provider that wants to keep their hardware and information intact in the case of a power surge or outage, since it gives them plenty of time to react until the problem is resolved and the primary power supply is restored.