High availability means having redundant hardware and software so that normal operations can continue after a single failure has occurred. Ideally, single failures do not interrupt operations at all, meaning that multiple instances of each component must be operational at all times so that the remaining component (or components) can take over the full load when any one component fails. In hardware devices, redundancy can be achieved by having redundant components within a single unit, or by having more than one unit installed and operational. If software redundancy is achieved by running the software simultaneously on more than one hardware device, the configuration is called active/active, because both components, or both units, are active at the same time. For this approach to be effective, the remaining components must be able handle the entire workload if a single component fails. The alternative approach for high availability is an active/passive configuration, in which the redundant component is not in use during normal operations but can be brought online if the component it is backing up fails.