Referring to a redundant system or processor that is not only turned on and warmed up, but is active and prepared to immediately assume the responsibilities of the primary system in the event it suffers a catastrophic failure. Synonymous with hot spare.
A hardware device that is connected to the computer or computer complex and remains powered on. It is ready to take over immediately if the primary unit fails. A hot standby may refer to a complete computer system; for example, a standby server, or a component in a computer such as a power supply or hard disk. See fault tolerant.