==Non-computer usage of the term==
The term may also be used to define replacement criteria for other components available from multiple sources. For example, a plug-compatible cooling fan may need to have not only the same physical size and shape, but also similar capability, run from the same voltage, use similar power, attach with a standard electrical connector, and have similar mounting arrangements. Some non-conforming units may be re-packaged or modified to meet plug-compatible requirements, as where an adapter plate is provided for mounting, or a different tool and instructions are supplied for installation, and these modifications would be reflected in the [[bill of materials]] for such components. Similar issues arise for computer system interfaces when competitors wish to offer an easy upgrade path.▼
In general, plug-compatible systems are designed where industry or [[de facto standard]]s have rigorously defined the environment, and there is a large installed population of machines that can benefit from third-party enhancements. ''Plug compatible'' does not mean identical replacement. However, nothing prevents a company from developing follow-on products that are backwards compatible with its own early products.