The UPS and the diesel generator are two instruments for keeping a server operational if there are problems with the main power source - an outage or unstable current which cannot keep the machine functioning properly, for instance. UPS is an abbreviation for Uninterruptible Power Supply, though it is sometimes called Uninterruptible Power Source also. The UPS is, basically, a highly effective battery that is attached to the server and to the power network constantly, so in case of any disturbance, it is already operating, which enables the server to continue doing the job without losing any info. The diesel generator is an engine which will power up the whole data center. It needs some time to start working and it's the UPS which gives it that time. These two power solutions are fundamental for any facility or hosting company that wants to avoid data loss and hardware damage as a consequence of an unexpected electrical power issue.