"Power failures are a fact of life, and as diligent, conscientious network admins, we implement whatever power backups we can wrangle funding for. A number of bad things can happen with a sudden power interruption: data corruption, mangled file systems, and even hardware damage. At the very least, we need to give important systems a chance to shut down gracefully, and then start back up when the power returns.
"This is exactly what a UPS--uninterruptible power supply--is designed for. The term 'uninterruptible power supply' is a bit misleading, though, as there are actually two types of UPS: lower-cost models that provide a battery backup and higher-end models that supply power continuously. The lower-end products, which used to be called 'SPS' (standby power supply) units, provide a battery backup that activates during a power interruption.
"The higher-end models, on the other hand, supply power continuously, and are truly 'uninterruptible.' They also 'condition' the power, smoothing out sags and spikes. The electricity that comes out of our outlets is rather grotty--it isn't the nice, clean, carefully controlled voltages that computers prefer; rather it arrives in lumps and bumps. While mostly unnoticed by the casual user, even little tiny sags and surges in electricity take their toll over time. A true UPS costs 50-100% more than its SPS cousins, and the batteries must be replaced more often..."
