UPS
Also known as: Uninterruptible Power Supply · Battery Backup
A UPS is a battery unit placed between the power outlet and connected equipment that takes over instantly and without interruption during a power outage.
An uninterruptible power supply, or UPS, sits between the wall outlet and the connected equipment and, during a power outage or voltage fluctuation, switches to its built-in battery without a noticeable interruption. It exists because a sudden power cut can damage servers and networking equipment and can corrupt data mid-write.
In practice, the UPS usually sits directly in the server rack, taking up one or more rack units, and depending on its size and the connected load bridges anywhere from a few minutes to about an hour. That is normally enough time to shut servers down cleanly, or to bridge until a backup generator takes over.
A common misconception is treating a UPS purely as surge or lightning protection: it often includes that as a side feature, but its actual purpose is bridging power from its own battery capacity. Another mistake is a UPS without an automatic shutdown routine for the servers, so the battery bridges the outage but the equipment still shuts down hard once it runs out.
What it means in practice
A server without a UPS usually only reveals the problem after the first power outage, when data turns out corrupted or a device no longer starts cleanly afterward. NDVDL sizes UPS capacity so servers can shut down in a controlled way during an outage instead of simply cutting off.
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