The UPS and the diesel generator are two means for keeping a server functioning if there are problems with the primary power supply - a disruption or shaky current which cannot keep the server functioning properly, for instance. UPS is an abbreviation for Uninterruptible Power Supply, though it can often be called Uninterruptible Power Source as well. The UPS is, in simple terms, a powerful battery that is attached to the web server and to the electricity network all of the time, so if there is any interruption, it's already functioning, which allows the server to carry on operating without losing any info. The diesel generator is an engine which can power up an entire data center. It needs some time to start working and it is the UPS which provides this time. Those two power solutions are fundamental for any facility or provider that wants to avoid info loss and hardware damage resulting from an unexpected electrical power problem.