The UPS and the diesel generator are two devices for keeping a server operational in case there are troubles with the primary power source - an interruption or unreliable current that can't keep the hosting server functional, for example. UPS is an abbreviation for Uninterruptible Power Supply, though it is frequently referred to as Uninterruptible Power Source also. The UPS is, basically, a powerful battery that's connected to the web server and to the power network all of the time, so if there is any disruption, it is already functioning, which enables the web server to keep on working without losing any information. The diesel generator is an engine which can power up the whole data center. It does take some time to begin working and it is the UPS which provides that time. These 2 power solutions are an absolute necessity for any facility or provider that wants to avoid info loss and hardware damage caused by an unexpected electric power problem.