The UPS and the diesel generator are two means for keeping a server operational if there are troubles with the main power supply - an interruption or unstable current which cannot keep the machine working correctly, for instance. UPS is an abbreviation for Uninterruptible Power Supply, even though it can often be called Uninterruptible Power Source as well. The UPS is, essentially, a highly effective battery which is attached to the web server and to the electricity network at all times, so in case of any interruption, it's already operating, which allows the hosting server to continue working without losing any data. The diesel generator is an engine which will power up a whole data center. It does take some time to begin working and it is the UPS which gives it this time. These two power solutions are a necessity for any facility or service provider that wants to prevent information loss and hardware damage caused by an unexpected electric power problem.