The UPS and the diesel generator are 2 devices for keeping a web server operational in case there are difficulties with the main source - an interruption or unstable current that can't keep the server functioning properly, for instance. UPS is an abbreviation for Uninterruptible Power Supply, though it is sometimes called Uninterruptible Power Source too. The UPS is, basically, a highly effective battery that is attached to the server and to the electricity network constantly, so in case there is any interruption, it's already working, that permits the web server to keep on working without losing any information. The diesel generator is an engine that can power up the entire data center. It does take some time to start working and it is the UPS which gives it this time. These two power solutions are a requirement for any facility or hosting company that wants to prevent info loss and hardware damage as a result of an unexpected electric power problem.