Many UPSs now offer a software component that enables you to automate backup and
shut down procedures in case there's a power failure while you're away from the
computer. There are two distinct types of UPS: off-line and line-interactive
(also called on-line).
An off-line UPS remains idle until a power failure occurs, and then switches
from utility power to its own power source, almost instantaneously. An on-line
UPS continuously powers the protected load from its reserves (usually lead-acid
batteries), while simultaneously replenishing the reserves from the AC power.
The on-line type of UPS, in addition to providing protection against complete
failure of the utility supply, provides protection against all common power
problems, and for this reason it is also known as a power conditioner and a
line conditioner.
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