The UPS and the diesel generator are two means for keeping a server working if there are difficulties with the main source - an outage or unstable current which cannot keep the hosting server working correctly, for instance. UPS is an abbreviation for Uninterruptible Power Supply, though it can often be referred to as Uninterruptible Power Source as well. The UPS is, essentially, a powerful battery that is attached to the web server and to the power network constantly, so in case of any disruption, it's already operating, which allows the web server to keep on doing the job without losing any data. The diesel generator is an engine that can power up the entire data center. It does take some time to begin working and it is the UPS that gives it this time. These 2 power solutions are an absolute necessity for any facility or service provider that wants to avoid information loss and hardware damage resulting from an unexpected electrical power issue.